Intersection testing in a ray tracing system using ray bundle vectors

ABSTRACT

Ray tracing systems and computer-implemented methods are described for performing intersection testing on a bundle of rays with respect to a box. Silhouette edges of the box are identified from the perspective of the bundle of rays. For each of the identified silhouette edges, components of a vector providing a bound to the bundle of rays are obtained and it is determined whether the vector passes inside or outside of the silhouette edge. Results of determining, for each of the identified silhouette edges, whether the vector passes inside or outside of the silhouette edge, are used to determine an intersection testing result for the bundle of rays with respect to the box.

CROSS-REFERENCE TO RELATED APPLICATIONS AND CLAIM OF PRIORITY

This application is a continuation under 35 U.S.C. 120 of copendingapplication Ser. No. 16/914,684 filed Jun. 29, 2020.

FIELD

The present disclosure is directed to techniques of performingintersection testing in a ray tracing system.

BACKGROUND

Ray tracing is a computational rendering technique for generating animage of a scene (e.g. a 3D scene) by tracing paths of light (‘rays’)from the viewpoint of a camera through the scene. Each ray is modelledas originating from the camera and passing through a pixel into thescene. As a ray traverses the scene it may intersect objects within thescene. The interaction between a ray and an object it intersects can bemodelled to create realistic visual effects. For example, in response todetermining an intersection of a ray with an object, a shader program(i.e. a portion of computer code) may be executed in respect of theintersection. A programmer can write the shader program to define howthe system reacts to the intersection which may, for example cause oneor more secondary rays to be emitted into the scene, e.g. to represent areflection of the ray off the intersected object or a refraction of theray through the object (e.g. if the object is transparent ortranslucent). As another example, the shader program could cause one ormore rays to be emitted into the scene for the purposes of determiningwhether the object is in shadow at the intersection point. The result ofexecuting the shader program (and processing the relevant secondaryrays) can be the calculation of a colour value for the pixel the raypassed through.

In order to reduce the number of intersection tests that need to beperformed, ray tracing systems can generate acceleration structures,wherein each node of an acceleration structure represents a regionwithin the scene. Acceleration structures are often hierarchical (e.g.having a tree structure) such that they include multiple levels ofnodes, wherein nodes near the top of the acceleration structurerepresent relatively large regions in the scene (e.g. the root node mayrepresent the whole scene), and nodes near the bottom of theacceleration structure represent relatively small regions in the scene.A “tree node” refers to a node which has pointers to other nodes in thehierarchical acceleration structure (i.e. a tree node has child nodes inthe hierarchical acceleration structure). A “leaf node” refers to a nodewhich has one or more pointers to one or more primitives (i.e. a leafnode does not have child nodes in the hierarchical accelerationstructure). In other words, leaf nodes of the acceleration structurerepresent regions bounding one or more objects in the scene. Theacceleration structure can have different structures in differentexamples, e.g. a grid structure, an octree structure, a spacepartitioning structure (e.g. a k-d tree) or a bounding volume hierarchy.The nodes can represent suitable shapes or regions in the scene (whichmay be referred to herein as “boxes”). In some examples the nodesrepresent axis-aligned bounding boxes (AABBs) in the scene.

Intersection testing can be performed for a ray (e.g. in a recursivemanner) using the acceleration structure by first testing the ray forintersection with the root node of the acceleration structure. If theray is found to intersect a parent node (e.g. the root node), testingcan then proceed to the child nodes of that parent. In contrast, if theray is found not to intersect a parent node, intersection testing of thechild nodes of that parent node can be avoided, saving computationaleffort. If a ray is found to intersect with a leaf node then it can betested against the objects within the region represented by the leafnode to thereby determine which object(s) the ray intersects with. Ifmore than one intersection is found for a ray then the closest of theintersection points to the ray's origin (i.e. the first intersectionthat the ray encounters in the scene) can be identified and the ray isdetermined to intersect at this identified closest intersection. The useof an acceleration structure (rather than testing rays directly withobjects in the scene) reduces the number of intersection tests that needto be performed, and simplifies the intersection tests. The intersectiontests are simpler because the nodes of the acceleration structurerepresent basic shapes (e.g. axis-aligned bounding boxes or spheres) forwhich intersection tests are simpler than for more complex objectshapes, e.g. defined in terms of triangular primitives for which theorientation is not predetermined.

SUMMARY

This summary is provided to introduce a selection of concepts that arefurther described below in the detailed description. This summary is notintended to identify key features or essential features of the claimedsubject matter, nor is it intended to be used to limit the scope of theclaimed subject matter.

There is provided a computer-implemented method of performingintersection testing in a ray tracing system, the method comprising:

-   -   receiving a bundle of rays to be tested for intersection with a        box;    -   identifying silhouette edges of the box from the perspective of        the bundle of rays;    -   for each of the identified silhouette edges:        -   obtaining components of a vector providing a bound to the            bundle of rays; and        -   determining whether the vector passes inside or outside of            the silhouette edge;    -   and    -   using results of determining, for each of the identified        silhouette edges, whether the vector passes inside or outside of        the silhouette edge, to determine an intersection testing result        for the bundle of rays with respect to the box.

For each of the identified silhouette edges, said obtaining componentsof a vector may comprise obtaining components of a single vectorproviding a single bound to the bundle of rays.

For each of the identified silhouette edges, the vector for which it isdetermined whether the vector passes inside or outside of the silhouetteedge may be the only vector for which a determination is made for thebundle of rays as to whether the vector passes inside or outside of thesilhouette edge.

The intersection testing result for the bundle of rays with respect tothe box may be determined using said results of determining, for each ofthe identified silhouette edges, whether the vector passes inside oroutside of the silhouette edge, and without using any other results ofdetermining whether any other vectors pass inside or outside of thesilhouette edges.

For each of the identified silhouette edges, said vector may provide anexternal bound to the bundle of rays with respect to said identifiedsilhouette edge, such that if it does not pass outside the identifiedsilhouette edge then it is known that none of the rays of the bundlepass outside said identified silhouette edge. If it is determined that,for each of the identified silhouette edges, the vector passes insidethe respective identified silhouette edge, then the intersection testingresult for the bundle of rays with respect to the box may be that all ofthe rays in the bundle of rays intersect the box. If it is determinedthat, for one or more of the identified silhouette edges, the vectorpasses outside the respective identified silhouette edge, then theintersection testing result for the bundle of rays with respect to thebox may not be that all of the rays in the bundle of rays intersect thebox. If the intersection testing result for the bundle of rays withrespect to the box is not that all of the rays in the bundle of raysintersect the box, then the method further may comprise determiningwhether any of the rays in the bundle of rays intersect the box.

For each of the identified silhouette edges, said vector may provide aninternal bound to the bundle of rays with respect to said identifiedsilhouette edge, such that if it does not pass inside the identifiedsilhouette edge then it is known that none of the rays of the bundlepass inside said identified silhouette edge. If it is determined that,for each of the identified silhouette edges, the vector passes insidethe respective identified silhouette edge, then the intersection testingresult for the bundle of rays with respect to the box may not be thatall of the rays in the bundle of rays miss the box. If it is determinedthat, for one or more of the identified silhouette edges, the vectorpasses outside the respective identified silhouette edge, then theintersection testing result for the bundle of rays with respect to thebox may be that all of the rays in the bundle of rays miss the box. Ifthe intersection testing result for the bundle of rays with respect tothe box is not that all of the rays in the bundle of rays miss the box,then the method may further comprise determining which of the rays inthe bundle of rays intersect the box.

The box may be an axis-aligned bounding box.

The method may further comprise:

-   -   performing a direction check to determine whether the box is        behind an origin of the bundle of rays, wherein if the direction        check determines that the box is behind the origin of the bundle        of rays then the intersection testing result is that the bundle        of rays misses the box; and/or    -   performing a distance check to determine whether the bundle of        rays terminates at a point in front of the box, wherein if the        distance check determines that the bundle of rays terminates at        a point in front of the box then the intersection testing result        is that the bundle of rays misses the box.

The obtained components of the vector providing a bound to the bundle ofrays may be the same as components of a direction vector of one of therays of the bundle.

Said obtained components of the vector providing a bound to the bundleof rays may be chosen from a set of component values comprising aminimum component value and a maximum component value in each dimensionof direction vectors of the rays in the bundle of rays.

All of the rays of the bundle of rays may have the same origin. For eachof the identified silhouette edges, said determining whether the vectorpasses inside or outside of the silhouette edge may comprise performinga comparison in accordance with(p_(o,i)−o_(i))d_(j)<(p_(o,j)−o_(j))d_(i), wherein p_(o,i) is the i^(th)component of a point on a first plane representing a first of the sidesof the box which forms the silhouette edge, p_(o,j) is the j^(th)component of a point on a second plane representing a second of thesides of the box which forms the silhouette edge, o_(i) and o_(j) arethe i^(th) and j^(th) components of the origin of the rays of the bundleof rays, and d_(i) and d_(j) are the obtained i^(th) and j^(th)components of the vector providing a bound to the bundle of rays.Performing a comparison “in accordance with”(p_(o,i)−o_(i))d_(j)<(p_(o,j)−o_(j))d_(i) includes performingcomparisons using mathematically equivalent equations, for example

$\left( {p_{o,i} - o_{i}} \right) < {\left( {p_{o,j} - o_{j}} \right){\frac{d_{i}}{d_{j}}.}}$

It might not be the case that all of the rays of the bundle of rays havethe same origin. For each of the identified silhouette edges, saiddetermining whether the vector passes inside or outside of thesilhouette edge may comprise performing a comparison in accordance with(p_(o,i)−o_(i,[min,max]))d_(j)<(p_(o,j)−o_(j,[min,max]))d_(i), whereinp_(o,i) is the i^(th) component of a point on a first plane representinga first of the sides of the box which forms the silhouette edge, p_(o,j)is the j^(th) component of a point on a second plane representing asecond of the sides of the box which forms the silhouette edge,o_(i,[min,max]) is either the minimum or the maximum of the i^(th)components of the origins of the rays of the bundle of rays,o_(j,[min,max]) is either the minimum or the maximum of the j^(th)components of the origins of the rays of the bundle of rays, and d_(i)and d_(j) are the obtained i^(th) and j^(th) components of the vectorproviding a bound to the bundle of rays. As above, performing acomparison “in accordance with”(p_(o,i)−o_(i,[min,max]))d_(j)<(p_(o,j)−o_(j,[min,max]))d_(i) includesperforming comparisons using mathematically equivalent equations, forexample

$\left( {p_{o,i} - o_{i{\lbrack{\min,\max}\rbrack}}} \right) < {\left( {p_{o,j} - o_{j,{\lbrack{\min,\max}\rbrack}}} \right){\frac{d_{i}}{d_{j}}.}}$

The method may further comprise: receiving rays; and constructingbundles of rays from the received rays to be tested for intersectionwith the box. Said constructing bundles of rays may comprise groupingtogether received rays based on their similarity.

Said constructing bundles of rays may comprise:

-   -   maintaining a set of open bundles to which new rays can be        added; and    -   for each of the received rays:        -   determining a level of similarity of the received ray with            each of the open bundles;        -   identifying a best match open bundle of said set of open            bundles for the received ray based on the determined levels            of similarity; and        -   if the determined level of similarity of the received ray            with the best match open bundle is above a threshold, adding            the received ray to the best match open bundle.

The method may further comprise, for each of the received rays:

-   -   if the determined level of similarity for the best match open        bundle is below the threshold, creating a new bundle and adding        the received ray to the new bundle.

Said received rays from which the bundles are constructed may: (i)include new rays which have not previously been included in a bundle ofrays, but (ii) not include rays which have previously been included in abundle of rays.

Said received rays from which the bundles are constructed may include:

-   -   new rays which have not previously been included in a bundle of        rays, and    -   rays which have previously been included in a bundle of rays        which has been deconstructed.

Data for a bundle of rays may be stored in a data structure and maycomprise:

-   -   origin data for the bundle of rays;    -   vector data describing the components of the vectors providing        the bounds to the bundle of rays; and    -   one or more pointers to ray data for the rays of the bundle of        rays.

The method may further comprise:

-   -   forming packets comprising one or both of indications of rays        and indications of bundles of rays which will require access to        the same block of memory for performing intersection testing;        and    -   fetching data from the block of memory for performing        intersection testing on the one or both of rays and bundles of        rays indicated by the indications in the packet.

The method may further comprise splitting up a bundle of rays intoindividual rays if a splitting metric is satisfied, wherein thesplitting metric may be based on one or more of:

-   -   a number of rays in the bundle of rays;    -   a spread of the rays in the bundle of rays;    -   a size of an area defined by the silhouette edges of the box;    -   whether the source of the rays in the bundle of rays is a frame        shader or a ray shader; and    -   data provided by the shader which created the rays in the bundle        of rays.

There is provided a ray tracing system comprising:

-   -   a tester module configured to receive a bundle of rays to be        tested for intersection with a box, wherein the tester module        comprises:        -   a set of one or more testing blocks configured to perform            intersection testing on the received bundle of rays with            respect to the box by:            -   identifying silhouette edges of the box from the                perspective of the bundle of rays;            -   for each of the identified silhouette edges:                -   obtaining components of a vector providing a bound                    to the bundle of rays; and                -   determining whether the vector passes inside or                    outside of the silhouette edge; and            -   using results of determining, for each of the identified                silhouette edges, whether the vector passes inside or                outside of the silhouette edge, to determine an                intersection testing result for the bundle of rays with                respect to the box.

A testing block of said set of one or more testing blocks may beconfigured to perform intersection testing for a bundle of rays and toperform intersection testing for a single ray.

The tester module may further comprise a results processor configured toprocess the intersection testing result for the bundle of rays withrespect to the box.

The tester module may further comprise a memory configured to store datadescribing the box which has been fetched from a memory for performingsaid intersection testing with respect to the box.

The ray tracing system may further comprise a bundle builder configuredto:

-   -   receive rays; and    -   group received rays together based on their similarity to        thereby construct bundles of rays to be tested for intersection        with the box.

There is provided a ray tracing system configured to perform any of themethods described herein.

There is described herein a ray tracing system comprising:

-   -   a tester module configured to receive a bundle of rays to be        tested for intersection with a box, wherein the tester module        comprises:        -   a first testing block configured to perform a first bundle            intersection test to determine whether or not all of the            rays of the bundle intersect the box, wherein if the first            bundle intersection test determines that all of the rays of            the bundle intersect the box, an intersection testing result            for the bundle with respect to the box is that all of the            rays of the bundle intersect the box; and        -   a second testing block configured to perform a second bundle            intersection test to determine whether or not all of the            rays of the bundle miss the box, wherein if the second            bundle intersection test determines that all of the rays of            the bundle miss the box, the intersection testing result for            the bundle with respect to the box is that all of the rays            of the bundle miss the box, and    -   wherein the tester module is configured to, if the first bundle        intersection test does not determine that all of the rays of the        bundle intersect the box and if the second bundle intersection        test does not determine that all of the rays of the bundle miss        the box:        -   split the bundle of rays up into individual rays; and        -   perform intersection tests for the individual rays with            respect to the box to determine which of the individual rays            intersect the box.

There is described herein a computer-implemented method of performingintersection testing in a ray tracing system, the method comprising:

-   -   receiving a bundle of rays to be tested for intersection with a        box;    -   performing a first bundle intersection test to determine whether        or not all of the rays of the bundle intersect the box, wherein        if the first bundle intersection test determines that all of the        rays of the bundle intersect the box, an intersection testing        result for the bundle with respect to the box is that all of the        rays of the bundle intersect the box; and    -   if the first bundle intersection test does not determine that        all of the rays of the bundle intersect the box, using a result        of performing a second bundle intersection test, which        determines whether or not all of the rays of the bundle miss the        box, to determine the intersection testing result for the bundle        with respect to the box,    -   wherein if the result of performing the second bundle        intersection test indicates that all of the rays of the bundle        miss the box, the intersection testing result for the bundle        with respect to the box is that all of the rays of the bundle        miss the box, and    -   wherein if the first bundle intersection test does not determine        that all of the rays of the bundle intersect the box and if the        result of performing the second bundle intersection test does        not indicate that all of the rays of the bundle miss the box,        then the method further comprises:        -   splitting the bundle of rays up into individual rays; and        -   performing intersection tests for the individual rays with            respect to the box to determine which of the individual rays            intersect the box.

The ray tracing systems described herein may be embodied in hardware onan integrated circuit. There may be provided a method of manufacturing,at an integrated circuit manufacturing system, a ray tracing system.There may be provided an integrated circuit definition dataset that,when processed in an integrated circuit manufacturing system, configuresthe system to manufacture a ray tracing system. There may be provided anon-transitory computer readable storage medium having stored thereon acomputer readable description of a ray tracing system that, whenprocessed in an integrated circuit manufacturing system, causes theintegrated circuit manufacturing system to manufacture an integratedcircuit embodying a ray tracing system.

There may be provided an integrated circuit manufacturing systemcomprising: a non-transitory computer readable storage medium havingstored thereon a computer readable description of the ray tracingsystem; a layout processing system configured to process the computerreadable description so as to generate a circuit layout description ofan integrated circuit embodying the ray tracing system; and anintegrated circuit generation system configured to manufacture the raytracing system according to the circuit layout description.

There may be provided computer program code for performing any of themethods described herein. There may be provided non-transitory computerreadable storage medium having stored thereon computer readableinstructions that, when executed at a computer system, cause thecomputer system to perform any of the methods described herein.

The above features may be combined as appropriate, as would be apparentto a skilled person, and may be combined with any of the aspects of theexamples described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described by way of example with reference tothe accompanying drawings. In the drawings:

FIG. 1 shows a schematic illustration of an edge test to determinewhether a ray intersects a 2D box;

FIG. 2 shows a schematic illustration of a three-dimensional box againstwhich rays are to be intersection tested;

FIG. 3 shows a first example ray tracing system;

FIG. 4 is a flow chart for a first method of performing intersectiontesting in a ray tracing system;

FIG. 5 shows three example bundles of rays to be tested for intersectionwith respect to a two dimensional box;

FIG. 6 shows three example bundles of rays to be tested for intersectionwith respect to a three dimensional box;

FIG. 7 illustrates another example of a bundle of rays to be tested forintersection with respect to a two dimensional box;

FIGS. 8 a and 8 b show two more examples of a three dimensional box asviewed from different perspectives;

FIG. 9 shows a second example ray tracing system;

FIG. 10 is a flow chart for a method of processing rays to be tested forintersection in a ray tracing system;

FIG. 11 is a flow chart for a method of performing intersection testingon a bundle of rays with respect to a box in a ray tracing system;

FIG. 12 is a flow chart for another method of performing intersectiontesting on a bundle of rays with respect to a box in a ray tracingsystem;

FIG. 13 a shows an example data structure for storing data of a ray;

FIG. 13 b shows an example data structure for storing data of a bundleof rays;

FIG. 14 shows a computer system in which a ray tracing system isimplemented;

FIG. 15 shows an integrated circuit manufacturing system for generatingan integrated circuit embodying a ray tracing system as described herein

FIG. 16 a illustrates a bundle of rays with differing origins to betested for intersection with respect to a box in a 2D example;

FIG. 16 b illustrates the bundle of rays shown in FIG. 16 a being testedin an AnyHit test for intersection with respect to the box by increasingthe effective size of the box;

FIG. 16 c illustrates the bundle of rays shown in FIG. 16 a being testedin an AllHit test for intersection with respect to the box by decreasingthe effective size of the box; and

FIG. 17 shows three example bundles of rays to be tested forintersection with respect to two 2D boxes.

The accompanying drawings illustrate various examples. The skilledperson will appreciate that the illustrated element boundaries (e.g.,boxes, groups of boxes, or other shapes) in the drawings represent oneexample of the boundaries. It may be that in some examples, one elementmay be designed as multiple elements or that multiple elements may bedesigned as one element. Common reference numerals are used throughoutthe figures, where appropriate, to indicate similar features.

DETAILED DESCRIPTION

The following description is presented by way of example to enable aperson skilled in the art to make and use the invention. The presentinvention is not limited to the embodiments described herein and variousmodifications to the disclosed embodiments will be apparent to thoseskilled in the art. Embodiments are described by way of example only.

Even when an acceleration structure is used, the amount of work involvedin performing intersection testing in a ray tracing system is still verylarge. For example, ray tracing may be used for rendering an image of a3D scene, where the image may have of the order of a million pixels. Aprimary ray may be traced for each sample position. In some examples,there may be one sample position for each pixel position, whilst in someother examples there may be multiple sample positions for each pixelposition (e.g. to allow for processes such as multi-sample anti-aliasing(MSAA) to be performed when rendering the final pixel values). When aray intersects with an object in the scene, a shader can be executedwhich may result in the emission of another ray (i.e. a “secondary ray”)into the scene. Each primary ray may result in the emission of manysecondary rays, which are all traced through the scene to determinetheir intersections. Therefore, it would not be unusual for there to betens or hundreds of millions of rays traced through a scene forrendering an image. The complexity of scenes to be rendered tends toincrease as graphics rendering technology develops, so it would not beunusual for there to be thousands of objects in a scene, each of whichmay be represented by many primitives. Furthermore, the images beingrendered may represent frames of a sequence of frames which are to berendered in real-time, e.g. for a display to a user in real-time. Forexample, the user may be playing a game wherein the rendered imagesrepresent a user's view of the 3D scene as the user plays the game. Inorder for the sequence of frames to appear like a continuous stream ofvideo data, many frames may be rendered per second, e.g. 24, 30 or 60frames per second to give some examples. It can therefore be appreciatedthat the work involved in performing intersection testing in a raytracing system to render scenes to be output in real-time is vast.

One way to overcome this problem, and to perform ray tracing to renderscenes to be output in real-time would be to have one or moresupercomputers to perform all of the processing. This could beconsidered to be a ‘brute force’ approach. However, as well as an aim tohave high performance (to perform ray tracing to render scenes to beoutput in real-time), there are also competing aims of reducing the size(e.g. silicon area) and power consumption of the ray tracing system. Forexample, there may be an aim to implement the ray tracing system on amobile device, such as a tablet or smartphone, for which the acceptablesize and power consumption may be much lower than for a supercomputer.As such, when designing a ray tracing system, there may be a trade-offbetween performance, power consumption and area. Depending on how thistrade-off is implemented, examples described herein may allow theperformance to be increased without a significant increase to the powerconsumption and area (compared to the prior art described above in thebackground section). Alternatively, in a different implementation of thetrade-off, examples described herein may allow the power consumptionand/or size of the ray tracing system to be decreased withoutsignificantly decreasing the performance of the ray tracing system(compared to the prior art described above in the background section).Different implementations can be designed to target different points inthe trade-off between performance, power consumption and silicon area.

Often, when performing intersection testing for rays within a scene,many rays will be tested for intersection with respect to the same box(e.g. where the box represents a node in a hierarchical accelerationstructure). In some situations, rays can be grouped together into abundle of rays, and an intersection test can be performed for the bundleof rays. In a situation where the intersection testing results would bethe same for all of the rays within a bundle then, rather thanperforming all of the intersection tests for each of the individual rayswithin the bundle, it may be possible to perform fewer intersectiontests (e.g. one or two intersection tests) for the bundle of rays as awhole, and to use the result(s) of the test(s) to infer the intersectiontesting results for all of the rays in the bundle. In this situation,the test(s) used to infer intersection testing results for all of therays in a bundle are referred to as bundle intersection test(s). It willbe understood that the term ‘bundle intersection test’ does not refer tosimply performing a separate test for each individual ray in the bundle.Instead, a bundle intersection test, which is performed on a bundle ofrays, provides a bundle intersection testing result for the bundle as awhole, which may be used to infer intersection testing results thatapply to all of the rays in the bundle. For example, if we can guaranteethat all of the rays in a ray bundle have the same intersection testingresult (e.g. hit or miss) with respect to a box then the result can bedetermined for the bundle as a whole, and used as the intersectiontesting results for all of the rays of the bundle. In this way, separateintersection tests for individual rays within at least some of thebundles may be avoided. Therefore, performing intersection testing onbundles of rays can reduce the overall number of intersection tests thatare performed and can result in fewer accesses to memory for fetchingray data. As described in more detail below, the bundle intersectiontests in examples described herein allow a single vector to be testedwith respect to each silhouette edge of the box, to thereby provide anintersection testing result for the bundle. For example, for eachsilhouette edge of the box, a vector is obtained which provides a boundto the bundle of rays, and it can be determined whether that vectorpasses inside or outside of the silhouette edge. The results ofdetermining, for each silhouette edge, whether the respective vectorpasses inside or outside of the silhouette edge can be used to determinean intersection testing result for the bundle of rays with respect tothe box. By reducing (compared to the prior art) the number ofcalculations that need to be performed to determine whether the rays ofa bundle intersect with a box, the intersection testing results can bedetermined faster, i.e. the latency of the ray tracing system can bereduced (or in other words, the performance of the ray tracing systemcan be increased), and the power consumption of the ray tracing systemcan be reduced.

As described in more detail below, two types of bundle intersectiontests are described herein:

(i) A first bundle intersection test (which may be referred to herein asan “AllHit” intersection test) determines whether or not all of the raysof a bundle intersect a box. The first bundle intersection test mayprovide a binary outcome, such that there are only two possible resultsfrom the first bundle intersection test: either (i) the first bundleintersection test determines that all of the rays of the bundleintersect the box, or (ii) the first bundle intersection test does notdetermine that all of the rays of the bundle intersect the box.(ii) A second bundle intersection test (which may be referred to hereinas an “AnyHit” test) determines whether or not all of the rays of thebundle miss the box. In other words, the second bundle intersection testdetermines whether or not any of the rays of the bundle hit the box. Thesecond bundle intersection test may provide a binary outcome, such thatthere are only two possible results from the second bundle intersectiontest: either (i) the second bundle intersection test determines that allof the rays of the bundle miss the box, or (ii) the second bundleintersection test does not determine that all of the rays of the bundlemiss the box.

Very similar logic can be used to implement these two different types ofbundle intersection tests, but with different bounding vectors beingtested in respect of the respective silhouette edges of the box.Furthermore, in examples described below, the logic configured toperform these two types of bundle intersection tests can also correctlyperform intersection tests on individual rays (each of which may beconsidered to be a bundle comprising only one ray). In this way, the raytracing system does not need different dedicated testing blocks forperforming intersection testing on individual rays and for performingintersection testing on bundles of rays, i.e. the same testing blockscan be used for testing individual rays and bundles of rays. This isparticularly useful when the testing blocks are implemented in hardware(e.g. fixed-function circuitry) because it reduces the possibility ofbottlenecking in the system due to one type of testing block beingsaturated whilst another type of testing block is idle.

These first and second bundle intersection tests may be implementedseparately, and they can each provide a benefit in terms of reducing thenumber of intersection tests that need to be performed (where the sameresult (either hit or miss) would be found for all of the rays within abundle). However, in some examples, both of these two types of bundleintersection tests may be implemented in the same ray tracing system.This can be particularly beneficial as it can avoid performing separateintersection tests for individual rays both if all of the rays of thebundle hit a box and if all of the rays of the bundle miss the box. Insome examples, an AllHit test could be performed on a bundle of rayswith respect to a box, and if the AllHit test determines that all of therays of the bundle hit the box then the intersection testing result isthat all of the rays of the bundle hit the box. If the AllHit test doesnot determine that all of the rays of the bundle hit the box then theAnyHit test can be performed on the bundle with respect to the box. Ifthe AnyHit test determines that all of the rays of the bundle miss thebox then the intersection testing result is that all of the rays of thebundle miss the box. If the intersection testing result has not yet beenfound then individual intersection tests may be performed for each ofthe rays to the bundle with respect to the box. In this example, theAnyHit test is performed conditionally, based on the result of theAllHit test. This is an example of how the method may be implemented insoftware. In different examples (e.g. when the method is implemented inhardware, e.g. fixed function circuitry), the AllHit test and the AnyHittest could be performed in parallel. In these examples, the AnyHit testwould be performed irrespective of the result of the AllHit test.Performing the AllHit and AnyHit tests in parallel can reduce thelatency of the method.

There will now be described a general example approach to performingintersection testing where a single ray is tested against a box. This isuseful for going on to explain how a bundle of rays can be testedagainst a box. In a three dimensional (3D) example, the box is a 3Dvolume. In 3D examples, the box could be any suitable shape such as acuboid (e.g. a cube), a sphere, a cylinder, a cone, a pyramid, a prism,etc. In a two dimensional (2D) example, the box is a 2D area. In these2D examples, the box could be any suitable shape, such as a rectangle(e.g. a square), a circle, a triangle, a hexagon, etc. In examplesdescribed in detail herein, the edges of the box are aligned with theaxes of the space in which ray tracing is performed. For example, thebox may be an axis-aligned bounding box (AABB) and may correspond with anode of a hierarchical acceleration structure.

A ray can be expressed mathematically in vector form as:r=o+Td  (1)where r is the ray, o is the ray's origin with respect to the coordinatesystem being used and d is the direction vector for the ray, and T is ascalar.

A plane can be expressed vectorially as a set of points p such that:(p−p ₀)·n=0  (2)where p_(o) is a known point on the plane and n is the normal vector tothe plane. In other words, the set of points p satisfying equation (2)lie on the plane.

At an intersection between the ray and the plane r=p. The intersectiondistance between a ray origin and a plane (i.e. the distance between theray origin and the intersection of the ray and the plane) can be foundby combining equation (1) and equation (2) with r=p, and rearranging forT. In the example explained below, it is assumed that the plane isaxis-aligned, i.e. aligned with the coordinate system, and thus thenormal vector n contains only one non-zero component, which for anormalised vector is equal to 1 (although it is noted that in otherexamples, the planes defining the edges of the box might not beaxis-aligned). For generality, denoting the non-zero component of thenormal vector as the i^(th) component (so for a three-dimensionalexample, i∈x, y, z), the combination of equations (1) and (2) can berewritten as:o _(i) +Td _(i) −p _(oi)=0  (3)And hence:

$\begin{matrix}{T = \frac{p_{oi} - o_{i}}{d_{i}}} & (4)\end{matrix}$

FIG. 1 shows an example of two rays 101 and 103 and a box 105. In thisexample, the box is two-dimensional (2D) for ease of illustration, andis defined by the space enclosed by four bounding edges. As shown, ray101 intersects the box 105 and ray 103 does not intersect box 105.

To determine whether a ray intersects the 2D box 105, a side test onpoints A and B is performed, where A and B are at diametrically opposedcorners of the box 105. Each side test is performed to determine whatside of the point under test the ray passes on. In different examples,when the box is a 3D box, the side tests determine which side of an edgethe ray passes on.

For performing intersection testing against point A, two intersectiondistances for each ray are determined. These intersection distances aredenoted T_(x) and T_(y) in FIG. 1 . T_(x) is the distance between theorigin of the ray and the point where the ray has the same x componentas the point A; and T_(y) is the distance between the origin of the rayand the point where the ray has the same y component as the point A.

For intersecting rays, e.g. for the intersecting ray 101, being testedwith respect to point A:T _(y) ≤T _(x)  (5)

For the non-intersecting ray 103 being tested with respect to point A:T _(x) <T _(y)  (6)

Using the equation for T given by (4), it can be seen that thegeneralised inequality to be evaluated to determine what side of an edge(in a 3D example) or point (in a 2D example) a ray passes on is givenby:

$\begin{matrix}{\frac{p_{oi} - o_{i}}{d_{i}} \leq \frac{p_{oj} - o_{j}}{d_{j}}} & (7)\end{matrix}$

To avoid the cost of performing a division operation, inequality (7) canbe rewritten as:(p _(oi) −o _(i))d _(i)≤(p _(oj) −o _(j))d _(i)  (8)

In the example shown in FIG. 1 , point A is the bottom right corner ofthe box, i=y and j=x, and if the inequality (8) (or inequality (7)) istrue then the ray passes on the inside of point A, whereas if theinequality (8) (or inequality (7)) is false then the ray passes on theoutside of point A. A similar test is performed in respect of cornerpoint B which is the top left corner of the box 105 (i.e. diametricallyopposed to point A). For point B the values can be set as i=x and j=y(which is the opposite as for the test for point A), and if theinequality (8) (or inequality (7)) is true then the ray passes on theinside of point B, whereas if the inequality (8) (or inequality (7)) isfalse then the ray passes on the outside of point B. To determine thatthe ray intersects the box 105, the inequalities for both point A and Bmust be true, whereas if either inequality is false then it isdetermined that the ray does not intersect the box 105.

FIG. 2 shows an example of a 3D box 201 as viewed from the origin of aray to be tested for intersection with respect to the box 201. In thisexample, the box 201 is an axis-aligned bounding box (AABB). Since thebox 201 is axis-aligned, each of the edges of the box 201 is parallel toone of the x, y or z axes. The box is shown comprising a set ofsilhouette edges, labelled 1 to 6. A silhouette edge is an edge definingpart of the silhouette of the box. The silhouette edges are determinedfrom a line of sight along the direction of the ray vector, i.e. the boxis depicted as viewed from a viewpoint, e.g. positioned at the ray'sorigin and directed along the direction of the ray. In other words, thesilhouette edges, labelled 1 to 6 in FIG. 2 , are the edges of a 2Dprojection of the box 201 as viewed from the perspective of a raytravelling from its origin. The box 201 is a cuboid in the example shownin FIG. 2 , such that the box 201 has either four or six silhouetteedges depending upon the perspective from which the box is viewed. Thebox 201 shown in FIG. 2 is merely for illustration and could, forexample, represent the volume corresponding to a root note, a parentnode, a child node and/or a leaf node in an acceleration structure.

In this 3D example, the intersection of two planes forms a line ratherthan a point as in the 2D case. Thus, the side test, performed on a 3Dbox, is used to determine what side of a silhouette edge (which takesthe form of a line) the ray passes on, wherein the side test performedon a 3D box may be referred to herein as an “edge test”. To determinewhether a ray intersects the box 201, an intersection test is performedfor each of the silhouette edges 1 to 6. Each intersection testcomprises performing the comparison of values specified in inequality(8).

The box 201 is formed from six planes, wherein for each axis (x, y, z)two of the planes have a normal parallel to that axis, such that thecomponent value of those planes for that axis are constant across eachof the planes. Of the two parallel planes, one will have a highercomponent value along the relevant axis. Therefore, for each axis thereis a maximum and a minimum component value defined by the planesdefining the box 201. The minimum values along each axis (x_(min),y_(min) and z_(min)) can define a ‘minimum’ position as a vectorp_(min), where p_(min)=(x_(min), y_(min), z_(min)) and the maximumvalues along each axis (x_(max), y_(max) and z_(max)) can define a‘maximum’ position as a vector p_(max), where p_(max)=(x_(max), y_(max),z_(max)). Therefore, p_(min) and p_(max) are diametrically opposedcorner positions of the box 201 and can be used in inequality (8) forthe edge comparison tests.

To simplify the edge comparison tests, the vectors p′_(min) and p′_(max)can be defined (and e.g. pre-computed) as:p′ _(min) =p _(min) −o  (9)p′ _(max) =p _(max) −o  (10)

The vectors p′_(min) and p′_(max) represent the displacement between theray origin (o) and p_(min) and p_(max) respectively. As described above,because the box 201 is axis-aligned, it follows that there are twoplanes of the bounding box lying on each axis, i.e. two ‘x’ planes(planes having constant x components), two ‘y’ planes (planes havingconstant y components) and two ‘z’ planes (planes having constant zcomponents). The components of the vector p′_(min) represent thedisplacements in x, y and z components from the ray origin to theminimum x, y and z planes. The components of the vector p′_(max)represent the displacements in x, y and z components from the ray originto the maximum x, y and z planes.

Which of the minimum or maximum planes are chosen to evaluate inequality(8) will depend on which two planes intersect at the silhouette edgebeing tested.

Equations (9) and (10) can be used to re-write inequality (8) as:p′ _(i) d _(j) ≤p′ _(j) d _(i)  (11)where p′_(i)=p_(min,i)−o_(i) or p′_(i)=p_(max,i)−o_(i), andp′_(j)=p_(min,j)−o_(j) or p′_(j)=p_(max,j)−o_(j).

For example, silhouette edge 6 shown in FIG. 2 is along the intersectionbetween the minimum x plane (i.e. of the two planes which have constantx values, the plane having the smaller x value) and the maximum z plane(i.e. of the two planes which have constant z values, the plane havingthe larger z value). The ray will pass the intersection test based onedge 6 if the ray intersects with the maximum z plane before itintersects with the minimum x plane, i.e. ifp′_(max,z)d_(x)≤p′_(max,x)d_(z), where p′_(max,z)=p_(max,z)−o_(z) andp′_(min,z)=p_(min,x)−o_(x).

As another example, silhouette edge 2 shown in FIG. 2 is along theintersection between the maximum x plane (i.e. of the two planes whichhave constant x values, the plane having the larger x value) and themaximum y plane (i.e. of the two planes which have constant y values,the plane having the larger y value). The ray will pass the intersectiontest based on edge 2 if the ray intersects with the maximum x planebefore it intersects with the maximum y plane, i.e. ifp′_(max,x)d_(y)≤p′_(max,y)d_(x), where p′_(max,x)=p_(max,x)−o_(x) andp′_(max,y)=p_(max,y)−o_(y).

It will be apparent how to perform the tests for each of the sixsilhouette edges labelled 1 to 6 in FIG. 2 . If all six tests are passedthen it is determined that the ray intersects the box 201. However, ifany one or more of the six tests fails then it is determined that theray does not intersect with the box 201, i.e. the ray passes outside oneor more of the six silhouette edges.

Thus, to perform a ray intersection test for box 201, an edge test isperformed for each silhouette edge 1 to 6 to determine what side of eachof those edges the ray passes on, where each edge test involvesperforming an evaluation to determine whether the condition specified inequation (11) is true for the two planes forming the edge under test.

As described in more detail below, distance and direction checks mayalso be performed to check whether the ray's origin and direction aresuch that the ray is travelling away from the box, or whether the rayendpoint falls short of the box. If either the ray is travelling awayfrom the box, or the ray endpoint falls short of the box then the raydoes not intersect with the box, and there is no need to perform theedge tests on the silhouette edges of the box.

FIG. 3 shows an example of a ray tracing system for performingintersection testing. Ray tracing system 300 is configured to implementintersection testing of rays with boxes, e.g. axis-aligned boxes.

The ray tracing system 300 comprises a scheduler 301, request queue 303,memory 305 and a tester module 307. The tester module 307 comprises atest queue 309, a set of one or more testing blocks (denoted generallyat 311) and a results processor 313. The request queue 303 and the testqueue 309 may take the form of buffers, e.g. stacks (i.e.first-in-last-out (FILO) buffers) or first-in-first-out (FIFO) buffers.The testing blocks may be implemented as hardware units (e.g. usingfixed-function circuitry) or in software, for example as shader codeexecuted by a processing unit.

The scheduler 301 receives instructions to trace (i.e. to performintersection testing for) a set of one or more rays. The scheduler cancollect rays before the rays are issued to the request queue 303. Thescheduler 301 may do this to group rays which require access to the sameblock or portion of the memory 305. The block or portion of the memory305 may be a contiguous block of memory at a set of memory addresseswhich can be fetched from the memory 305 together. A group of rays thatreference the same block of the memory 305 may be referred to as apacket. For example, rays which are to be tested with respect to thesame box or object may be grouped into a packet, such that the data forthe box or object can be fetched once from the memory 305 for use in theintersection testing of all of the rays in the packet. As an example,for the initial stage of the intersection testing, it may be the casethat all rays will intersect the root node and thus require access tothe same block of memory 305 and so fall within one packet. Once thescheduler has assembled one or more rays into a packet, the schedulerwill issue the packet and cause the packet to join the request queue 303to request the node data for the packet (i.e. data describing a boxcorresponding to the appropriate node of the acceleration structureagainst which the rays of the packet are to be tested for intersection)from memory 305. The node data for the packet is then retrieved frommemory 305 and passed to the tester module 307.

At the tester module 307, the node data for a packet is received at thetest queue 309. The ray data for the packet is also received at thetester module. The ray data for the packet may be received from a memory(e.g. memory 305), or in other examples it may be received from requestqueue 303 (via a link, not shown in FIG. 3 ), to be associated with thecorresponding node data at test queue 309. The tester module 307allocates rays from the packet to the testing blocks 311. The testermodule 307 might allocate the rays sequentially. When a ray of thepacket has been allocated to a testing block, that testing blockperforms intersection testing to determine whether that ray intersectsthe box corresponding to the node that ray is being tested against, e.g.by performing edge tests for the appropriate edges of the box, e.g. forthe six silhouette edges of the box 201 labelled in FIG. 2 , asdescribed above.

The testing blocks each output the result of the intersection tests theyhave performed to the results processor 313. The results processor 313processes the results of the intersection tests. Specifically, if a rayhas been found to not intersect the node it was being tested against,the processor 313 does not schedule intersection tests for that ray inrespect of the child nodes of the node which was not intersected. If theresults processor 313 determines that a ray has intersected a node itwas being tested against, that ray is output from the tester module 307back to the scheduler 301, where it will be grouped into a packet andscheduled for intersection testing in respect of a child node of theintersected node.

The above-described process is repeated iteratively until the rays haveno more hits. In response to an intersection of a ray with a leaf node,objects within that leaf node (e.g. triangles) are each scheduled forintersection testing with the ray. The tester module 307 may compriseobject testing blocks (not shown in FIG. 3 ) configured to performintersection tests for the rays that intersect a leaf node in respect ofthe object(s) within that leaf node. The objects may be described withtriangular primitives, such that the object testing blocks areconfigured to test rays for intersection with respect to triangles inthe scene. A person skilled in the art would know how to test a ray forintersection with a triangular primitive, and the details of thisprocess are not described in detail herein. If the result of all theintersection testing for a ray is that the ray does not intersect withany objects in the scene then a ‘miss’ result is returned and can beprocessed accordingly. If the result of all the intersection testing fora ray is that the ray intersects with a single object then data for thisintersection can be returned with a ‘hit’ result and processedaccordingly. If the result of all the intersection testing for a ray isthat the ray intersects with more than one object then the intersectiondistances for the intersections (i.e. the distances from the ray originto the intersection points) are compared to find the ‘closest hit’, i.e.the intersection point closest to the ray origin (i.e. the intersectionpoint with the smallest value of T). Data for this closest hitintersection can be returned with a ‘hit result’ and processedaccordingly.

As described above, in examples described herein, rays can be groupedtogether into bundles, and then bundle intersection tests can beperformed on the bundles of rays. This can reduce the number ofintersection tests that need to be performed. The number of rays in abundle can vary. There may be a maximum number of rays that can beincluded in a bundle, and this maximum number of rays may be differentin different examples. For example, the maximum number of rays in abundle could be 4, 16 or 32 just to give three examples.

The method described above for performing intersection testing for anindividual ray with respect to a box can be extended to performintersection testing for a bundle of rays with respect to a box. Forexample, FIG. 4 is a flow chart for a method of performing intersectiontesting for a bundle of rays, which may be performed by the testermodule 307.

In step S402, a bundle of rays is received at the tester module 307. Thebundle of rays is to be tested for intersection with a box. An exampleprocess for grouping rays together to form bundles is described belowwith reference to the flow chart shown in FIG. 10 . In a first example,all of the rays within a bundle have the same origin (although in otherexamples the rays within a bundle may have different ray origins). Therays within a bundle can have different ray direction vectors. Vectorscan be defined for a bundle to provide bounds to the bundle of rays,i.e. to define edges of the bundle. The bounding vectors for a bundlemay tightly bound the rays within the bundle. For example, FIG. 5 showsa 2D example in which three bundles of rays (generally denoted 504, 506and 508 in FIG. 5 ) are to be tested for intersection with a 2D box 502.The first bundle of rays 504 has two vectors 504 ₁ and 504 ₂ whichprovide the bounds to the first bundle of rays; the second bundle ofrays 506 has two vectors 506 ₁ and 506 ₂ which provide the bounds to thesecond bundle of rays; and the third bundle of rays 508 has two vectors508 ₁ and 508 ₂ which provide the bounds to the third bundle of rays. Abundle of rays and an indication of the box are provided to a testingblock 311. Steps S404 to S416 may be performed by one of the testingblocks 311.

In step S404 a distance check and a direction check are performed for abundle of rays with respect to a box. In step S406 it is determinedwhether the bundle of rays pass the distance and direction checks. Thedirection check determines whether the box is behind an origin of thebundle of rays. In other words, when looking from an origin of thebundle of rays, along a direction within the range of directions boundedby the bounding vectors for the bundle of rays, the direction checkdetermines whether the box is behind the origin. For example, thedirection check may involve, for each component (i.e. each of the x, yand z components, denoted generally as the i^(th) component), if thecomponent of a particular one of the bounding vectors of the bundle(d_(i)) is positive, then checking whether the bundle origin has agreater component value (o_(i)) than the maximum component value of thebox (p_(max,i)); and if the component of a particular one of thebounding vectors of the bundle (d_(i)) is negative, then checkingwhether the bundle origin has a smaller component value (o_(i)) than theminimum component value of the box (p_(min,i)). If, for one or more ofthe components, either of these two conditions is satisfied then it canbe determined that the ray will not intersect the box without needing toperform edge tests on the silhouette edges of the box. The particularone of the bounding vectors of the bundle to choose in the directioncheck may depend upon whether the bundle intersection test is a firstbundle intersection test (i.e. an ‘AllHit’ test) which aims to determinewhether all of the rays of the bundle hit the box, or a second bundleintersection test (i.e. an ‘AnyHit’ test) which aims to determinewhether all of the rays of the bundle miss the box.

FIG. 17 shows a 2D example of two axis-aligned boxes: box 1702 (whichhas minimum and maximum components p_(min,a) and p_(max,a)) and box 1704which has minimum and maximum components p_(min,b) and p_(max,b)). FIG.17 also shows three bundles of rays: bundle 1706 which has boundingvectors 1706 ₁ and 1706 ₂ (both of which have negative x components),bundle 1708 which has bounding vectors 1708 ₁ (which has a negative xcomponent) and 1708 ₂ (which has a positive x component), and bundle1710 which has bounding vectors 1710 ₁ and 1710 ₂ (both of which havepositive x components). All of the bundles 1706, 1708 and 1710 havetheir origin at a position o. For example, for an AnyHit test, thedirection test is useful when the i^(th) component of all (e.g. both) ofthe bounding vectors of the bundle have the same sign (e.g. when thei^(th) component is the x component, that is true for bundles 1706 and1710, but not for bundle 1708). For example, if the bounding vector withthe smallest i^(th) component has a positive i^(th) component, implyingthat all of the bounding vectors have positive values for their i^(th)components (e.g. the bounding vectors of bundle 1710 all have positive xcomponents), then that bounding vector with the smallest i^(th)component (e.g. bounding vector 1710 ₁) is the “particular one” of thebounding vectors mentioned above. Because the i^(th) component of the“particular one” of the bounding vectors is positive, the directioncheck involves checking whether the bundle origin has a greatercomponent value (o_(i)) than the maximum component value of the box(p_(max,i)). For example, the x component value of bounding vector 1710₁ is positive, so the direction check involves checking whether the xcomponent of the bundle origin (o_(x)) is greater than the x componentsof p_(max,a) (for box 1702) and p_(max,b) (for box 1704). In the exampleshown in FIG. 17 the bundle 1710 will pass the direction check for anAnyHit test in respect of box 1704, but it will fail the direction checkfor an AnyHit test in respect of box 1702. If the bounding vector withthe largest i^(th) component has a negative i^(th) component, implyingthat all of the bounding vectors have negative values for their i^(th)components (e.g. the bounding vectors of bundle 1706 all have negative xcomponents), then that bounding vector with the largest i^(th) component(e.g. bounding vector 1706 ₂) is the “particular one” of the boundingvectors mentioned above. Because the i^(th) component of the “particularone” of the bounding vectors is negative, the direction check involveschecking whether the bundle origin has a smaller component value (o_(i))than the minimum component value of the box (p_(min,i)). For example,the x component value of bounding vector 1706 ₂ is negative, so thedirection check involves checking whether the x component of the bundleorigin (o_(x)) is smaller than the x components of p_(min,a) (for box1702) and p_(min,b) (for box 1704). In the example shown in FIG. 17 thebundle 1706 will pass the direction check for an AnyHit test in respectof box 1702, but it will fail the direction check for an AnyHit test inrespect of box 1704. For the AnyHit test, if the i^(th) components ofthe bounding vectors do not all have the same sign (e.g. for bundle1708, the bounding vector with the smallest x component does not have apositive x component and the bounding vector with the largest xcomponent does not have a negative x component) then the direction checkdoes not provide a determination of whether there may be an intersectionwith the box. In contrast, for the AllHit test, the direction test maybe useful even if the signs of the i^(th) components of the boundingvectors are not all the same. For example, for an AllHit test, if thebounding vector with the largest i^(th) component has an i^(th)component which is positive (e.g. when the i^(th) component is the xcomponent, that is true for bundles 1708 and 1710), then that boundingvector with the largest i^(th) component (e.g. bounding vector 1708 ₂for bundle 1708 and bounding vector 1710 ₂ for bundle 1710) is a“particular one” of the bounding vectors mentioned above. Because thei^(th) component of the “particular one” of the bounding vectors ispositive, the direction check involves checking whether the bundleorigin has a greater component value (o_(i)) than the maximum componentvalue of the box (p_(max,i)). For example, the x component values ofbounding vectors 1708 ₂ and 1710 ₂ are positive, so the direction checksfor bundles 1708 and 1710 involve checking whether the x component ofthe bundle origin (o_(x)) is greater than the x components of p_(max,a)(for box 1702) and p_(max,a) (for box 1704). In the example shown inFIG. 17 the bundles 1708 and 1710 will pass the first direction checkfor an AllHit test in respect of box 1704, but they will fail the firstdirection check for an AllHit test in respect of box 1702. Similarly,for an AllHit test, if the bounding vector with the smallest i^(th)component has an i^(th) component which is negative (e.g. when thei^(th) component is the x component, that is true for bundles 1706 and1708), then that bounding vector with the smallest i^(th) component(e.g. bounding vector 1706 ₁ for bundle 1706 and bounding vector 1708 ₁for bundle 1708) is a “particular one” of the bounding vectors mentionedabove. Because the i^(th) component of the “particular one” of thebounding vectors is negative, the direction check involves checkingwhether the bundle origin has a smaller component value (o_(i)) than theminimum component value of the box (p_(min,i)). For example, the xcomponent values of bounding vectors 1706 ₁ and 1708 ₁ are negative, sothe direction checks for bundles 1706 and 1708 involve checking whetherthe x component of the bundle origin (o_(x)) is smaller than the xcomponents of p_(min,a) (for box 1702) and p_(min,b) (for box 1704). Inthe example shown in FIG. 17 the bundles 1706 and 1708 will pass thesecond direction check for an AllHit test in respect of box 1702, butthey will fail the second direction check for an AllHit test in respectof box 1704. If a bundle fails either of the direction checks for anAllHit test then it is determined to fail the direction test, so in theexample shown in FIG. 17 bundle 1708 will fail the direction check foran AllHit test in respect of both boxes 1702 and 1704.

To summarise the direction checks:

-   -   for an All hit test, for each of the i^(th) components:        -   if the i^(th) component of either of the bounding vectors of            a bundle is negative then a miss is found if            p_(min,i)>o_(i); and        -   if the i^(th) component of either of the bounding vectors of            a bundle is positive then a miss is found if            p_(max,i)<o_(i); and    -   for an AnyHit test, for each of the i^(th) components:        -   if the i^(th) component of both of the bounding vectors of a            bundle are negative then a miss is found if p_(min,i)>o_(i);            and        -   if the i^(th) component of both of the bounding vectors of a            bundle are positive then a miss is found if p_(max,i)<o_(i).

The distance check determines whether the bundle of rays terminates at apoint in front of the box. A maximum distance that the rays of thebundle can travel in the scene before they are terminated (or “clipped”)may be provided in the data for a bundle of rays. If the distance checkdetermines that the bundle of rays terminates at a point in front of thebox (i.e. before it reaches the box) then it can be determined that theintersection testing result is that the bundle of rays misses the box,without needing to perform edge tests on the silhouette edges of thebox. For example, the distance check may involve, performing a check foreach component (i.e. each of the x, y and z components, denotedgenerally as the i^(th) component). The distance check may be determinedto fail if an inequality is satisfied for any of the components. Forexample, for an AnyHit test, if p_(min,i)>o_(i) then the distance checkcan determine, for each of the i^(th) components, which of the boundingvectors has the largest value for its i^(th) component and then it canbe determined whether p_(min,i)>o_(i)+T_(max)d_(i,max), where T_(max) isthe maximum value of T (i.e. the value of T at which the ray is clippedif it has not yet intersected with anything in the scene), whered_(i,max)=max(d_(i,1), d_(i,2)), and where d_(i,1) is the i^(th)component of the first bounding vector of the bundle and d_(i,2) is thei^(th) component of the second bounding vector of the bundle. In thisexample, the bundle has just two bounding vectors. In this example, ifp_(min,i)>o_(i)+T_(max)d_(i,max) then the distance check fails. For anAnyHit test, if p_(max,i)<o_(i) then the distance check can determine,for each of the i^(th) components, which of the bounding vectors has thesmallest value for its i^(th) component and then it can be determinedwhether p_(max,i)<o_(i)+T_(max)d_(i,min), whered_(i,min)=min(d_(i,1),d_(i,2)), and where d_(i,1) is the i^(th)component of the first bounding vector of the bundle and d_(i,2) is thei^(th) component of the second bounding vector of the bundle. In thisexample, the bundle has just two bounding vectors. In this example, ifp_(max,i)<o_(i)+T_(max)d_(i,min) then the distance check fails.

As another example, for an AllHit test, if p_(min,i)>o_(i) then thedistance check can determine, for each of the i^(th) components, whichof the bounding vectors has the smallest value for its i^(th) component(to thereby identify d_(i,min)) and then it can be determined whetherp_(min,i)>o_(i)+T_(max)d_(i,min). In this example, ifp_(min,i)>o_(i)+T_(max)d_(i,min) then the distance check fails. For anAllHit test, if p_(max,i)<o_(i) then the distance check can determine,for each of the i^(th) components, which of the bounding vectors has thelargest value for its i^(th) component (to thereby identify d_(i,max))and then it can be determined whether p_(max,i)<o_(i)+T_(max)d_(i,max).In this example, if p_(max,i)<o_(i)+T_(max)d_(i,max) then the distancecheck fails. In the examples of the distance checks described above, ifthe distance check fails then it is determined that the intersectiontesting result is that the bundle of rays misses the box, withoutneeding to perform edge tests on the silhouette edges of the box.

If either the distance check or the direction check is failed then themethod passes from step S406 to step S408. In step S408 the intersectiontesting result is determined to be that the bundle of rays misses thebox. This intersection testing result can be outputted from the testingblock 311 to the results processor 313, without steps S410 to S416 beingperformed.

If the distance check and the direction check are passed then the methodpasses from step S406 to step S410.

The distance and direction checks are optional, i.e. in some examplessteps S404 to S408 might not be performed. Performing the distance anddirection checks (in steps S404 to S408) can provide a reduction in thenumber of edge tests that need to be performed on the silhouette edges,because some intersection testing results (i.e. misses) can bedetermined by the distance and direction checks without needing toperform the edge tests for the silhouette edges.

In step S410 the testing block 311 identifies the silhouette edges ofthe box from the perspective of the bundle of rays.

Steps S412 and S414 are performed for each of the silhouette edgesidentified in step S410.

In step S412 components of a vector are obtained providing a bound tothe bundle of rays. The vector, of which components are obtained, isdependent upon a particular silhouette edge being tested, and componentsof different vectors may be obtained for different silhouette edges. Thecomponents of the vector may be “obtained” by determining (e.g.calculating) the components of the vector or by receiving (e.g. reading)the components of the vector. The vector may, or may not, be the same asa direction vector for one of the rays of the bundle. For example, thecomponents of the vector may be obtained by identifying, from thedirection vectors of the rays in the bundle of rays, a minimum componentvalue and a maximum component value in each dimension, wherein saidobtained components of the vector providing a bound to the bundle ofrays are chosen from a set of component values comprising the identifiedminimum component value and the identified maximum component value ineach dimension.

A vector may provide an external bound to a bundle of rays with respectto a silhouette edge in the sense that if it does not pass outside theidentified silhouette edge then it is known that none of the rays of thebundle pass outside the silhouette edge. Furthermore, a vector mayprovide an internal bound to a bundle of rays with respect to asilhouette edge in the sense that if it does not pass inside theidentified silhouette edge then it is known that none of the rays of thebundle pass inside the silhouette edge.

In step S414 the testing block 311 determines whether the vectorobtained in step S412 passes inside or outside of the silhouette edge inquestion. This may be done as described above in relation to the testingof a single ray with respect to a box, e.g. in accordance with theinequality (11) given above. In examples described herein, for each ofthe silhouette edges, a single vector is obtained in step S412 andtested in step S414. The choice of which bounding vector to test withrespect to each silhouette edge depends upon whether an AllHit test oran AnyHit test is being performed, as explained in more detail below.

In step S416, the results of determining, for each of the identifiedsilhouette edges, whether the vector passes inside or outside of thesilhouette edge, are used to determine an intersection testing resultfor the bundle of rays with respect to the box. For example, if thetests for all of the silhouette edges indicate that the respectivevectors pass inside the respective silhouette edges then in step S416the result of the bundle intersection test with respect to the box isdetermined to be a “hit” or a “pass”; whereas if the tests for one ormore of the silhouette edges indicate that the respective vector passesoutside the respective silhouette edge then in step S416 the result ofthe bundle intersection test with respect to the box is determined to bea “miss” or a “fail”. For an AnyHit test, a “pass” or a “hit” resultmeans that the test has not determined that all of the rays of thebundle miss the box, and a “fail” or “miss” results means that the testhas determined that all of the rays of the bundle miss the box. For anAllHit test, a “pass” or a “hit” result means the test has determinedthat all of the rays of the bundle hit the box, and a “fail” or “miss”results means that the test has not determined that all of the rays ofthe bundle hit the box.

For example, the bundle intersection test may be an AllHit test (whichmay be referred to as an “AnyMiss test”, e.g. if the outputs of the testwere inversed). As described above, there are only two possible resultsfrom an AllHit test: either (i) the AllHit test determines that all ofthe rays of the bundle intersect the box, or (ii) the AllHit test doesnot determine that all of the rays of the bundle intersect the box. Inthis example, for each of the identified silhouette edges, the vectorthat is obtained in step S412 provides an external bound to the bundleof rays with respect to the identified silhouette edge. The vectorprovides an external bound to the bundle of rays with respect to theidentified silhouette edge in the sense that if it does not pass outsidethe identified silhouette edge then it is known that none of the rays ofthe bundle pass outside the identified silhouette edge. As mentionedabove, the vector may have either the maximum or the minimum componentvalues of the ray direction vectors of the rays in the bundle in eachdimension. Whether the maximum or minimum component value is chosen ineach dimension depends upon the silhouette edge being tested and whetheran internal bound or an external bound is being provided by the vector.The resulting vector may or may not be the same as the direction vectorof one of the rays of the bundle.

If it is determined that, for each of the identified silhouette edges,the respective vector passes inside the identified silhouette edge, thenthe intersection testing result for the bundle of rays with respect tothe box is that all of the rays in the bundle of rays intersect the box.If it is determined that, for one or more of the identified silhouetteedges, the vector passes outside the respective identified silhouetteedge, then the intersection testing result for the bundle of rays withrespect to the box is not that all of the rays in the bundle of raysintersect the box, e.g. one or more of the rays of the bundle may missthe box.

For example, in the 2D example shown in FIG. 5 , an AllHit test may beperformed for the first bundle of rays 504 with respect to the 2D box502. In a 2D example, the silhouette edges reduce down to just twosilhouette points, denoted 510 ₁ and 510 ₂ in FIG. 5 . With respect tosilhouette point 510 ₁, the vector 504 ₁ is obtained (in step S412) forthe bundle 504 because this vector 504 ₁ provides an external bound tothe bundle 504 with respect to the silhouette point 510 ₁, i.e. if itdoes not pass outside the identified silhouette point 510 ₁ then it isknown that none of the rays of the bundle 504 pass outside theidentified silhouette point 510 ₁. It is determined in step S414 thatthe vector 504 ₁ passes inside the silhouette point 510 ₁. Inparticular, with respect to silhouette point 510 ₁ it is determined inaccordance with inequality (11) that(p_(min,x)−o_(x))d_(y,1)≤(p_(max,y)−o_(y))d_(x,1), where p_(min,x) andp_(max,y) are the x and y component values at point 510 ₁, o_(x) ando_(y) are the x and y component values of the origin of the bundle ofrays 504, and d_(x,1) and d_(y,1) are the x and y component values ofthe direction of vector 504 ₁. This single test determines that all ofthe rays of the ray bundle 504 pass inside the silhouette point 510 ₁ ofthe box 502. With respect to silhouette point 510 ₂, the vector 504 ₂ isobtained (in step S412) for the bundle 504 because this vector 504 ₂provides an external bound to the bundle 504 with respect to thesilhouette point 510 ₂. It is determined in step S414 that the vector504 ₂ passes inside the silhouette point 510 ₂. In particular, withrespect to silhouette point 510 ₂ it is determined in accordance withinequality (11) that (p_(min,y)−o_(y))d_(x,2)≤(p_(max,x)−o_(x))d_(y,2),where p_(max,x) and p_(min,y) are the x and y component values at point510 ₂, o_(x) and o_(y) are the x and y component values of the origin ofthe bundle of rays 504, and d_(x,2) and d_(y,2) are the x and ycomponent values of the direction of vector 504 ₂. This single testdetermines that all of the rays of the ray bundle 504 pass inside thesilhouette point 510 ₂ of the box 502. These two tests are sufficient todetermine that all of the rays of the bundle 504 hit the box 502.Therefore, in step S416, it is determined that the result of the AllHittest for the bundle of rays 504 with respect to the box 502 is that allof the rays of the bundle 504 hit the box 502.

As another example, in the 2D example shown in FIG. 5 , an AllHit testmay be performed for the second bundle of rays 506 with respect to the2D box 502. With respect to silhouette point 510 ₁, the vector 506 ₁ isobtained (in step S412) for the bundle 506 because this vector 506 ₁provides an external bound to the bundle 506 with respect to thesilhouette point 510 ₁. It is determined in step S414 that the vector506 ₁ passes inside the silhouette point 510 ₁. In particular, withrespect to silhouette point 510 ₁ it is determined in accordance withinequality (11) that (p_(min,x)−o_(x))d_(y,1)≤(p_(max,y)−o_(y))d_(x,1),where p_(min,x) and p_(max,y) are the x and y component values at point510 ₁, o_(x) and o_(y) are the x and y component values of the origin ofthe bundle of rays 506, and d_(x,1) and d_(y,1) are the x and ycomponent values of the direction of vector 506 ₁. This single testdetermines that all of the rays of the ray bundle 506 pass inside thesilhouette point 510 ₁ of the box 502. With respect to silhouette point510 ₂, the vector 506 ₂ is obtained (in step S412) for the bundle 506because this vector 506 ₂ provides an external bound to the bundle 506with respect to the silhouette point 510 ₂. It is determined in stepS414 that the vector 506 ₂ passes outside the silhouette point 510 ₂. Inparticular, with respect to silhouette point 510 ₂ it is determined thatthe bundle of rays 506 does not satisfy inequality (11). In other words,for the bundle of rays 506, it is not true that(p_(min,y)−o_(y))d_(x,2)≤(p_(max,x)−o_(x))d_(y,2), where p_(max,x) andp_(min,y) are the x and y component values at point 510 ₂, o_(x) ando_(y) are the x and y component values of the origin of the bundle ofrays 506, and d_(x,2) and d_(y,2) are the x and y component values ofthe direction of vector 506 ₂. This test does not determine that all ofthe rays of the ray bundle 506 pass inside the silhouette point 510 ₂ ofthe box 502. Therefore, in step S416, the result of the AllHit test forthe bundle of rays 506 with respect to the box 502 is not that all ofthe rays of the bundle 506 hit the box 502. In other words, the AllHittest does not guarantee that all of the rays of the bundle 506 hit thebox 502.

As another example, in the 2D example shown in FIG. 5 , an AllHit testmay be performed for the third bundle of rays 508 with respect to the 2Dbox 502. With respect to silhouette point 510 ₁, the vector 508 ₁ isobtained (in step S412) for the bundle 508 because this vector 508 ₁provides an external bound to the bundle 508 with respect to thesilhouette point 510 ₁. It is determined in step S414 that the vector508 ₁ passes inside the silhouette point 510 ₁. In particular, withrespect to silhouette point 510 ₁ it is determined in accordance withinequality (11) that (p_(min,x)−o_(x))d_(y,1)≤(p_(max,y)−o_(y))d_(x,1),where p_(min,x) and p_(max,y) are the x and y component values at point510 ₁, o_(x) and o_(y) are the x and y component values of the origin ofthe bundle of rays 508, and d_(x,1) and d_(y,1) are the x and ycomponent values of the direction of vector 508 ₁. This single testdetermines that all of the rays of the ray bundle 508 pass inside thesilhouette point 510 ₁ of the box 502. With respect to silhouette point510 ₂, the vector 508 ₂ is obtained (in step S412) for the bundle 508because this vector 508 ₂ provides an external bound to the bundle 508with respect to the silhouette point 510 ₂. It is determined in stepS414 that the vector 508 ₂ passes outside the silhouette point 510 ₂. Inparticular, with respect to silhouette point 510 ₂ it is determined thatthe bundle of rays 508 does not satisfy inequality (11). In other words,for the bundle of rays 508, it is not true that(p_(min,y)−o_(y))d_(x,2)≤(p_(max,x)−o_(x))d_(y,2), where p_(max,x) andp_(min,y) are the x and y component values at point 510 ₂, o_(x) ando_(y) are the x and y component values of the origin of the bundle ofrays 508, and d_(x,2) and d_(y,2) are the x and y component values ofthe direction of vector 508 ₂. This test does not determine that all ofthe rays of the ray bundle 508 pass inside the silhouette point 510 ₂ ofthe box 502. Therefore, in step S416, the result of the AllHit test forthe bundle of rays 508 with respect to the box 502 is not that all ofthe rays of the bundle 508 hit the box 502. In other words, the AllHittest does not guarantee that all of the rays of the bundle 508 hit thebox 502.

It can be seen that the result of the AllHit test is the same forbundles 506 and 508, i.e. it is not confirmed that all of the rays ineither bundle 506 or 508 hits the box 502. This is the case even thoughsome of the rays of bundle 508 do hit the box 502.

FIG. 6 shows a 3D example in which three bundles of rays (generallydenoted 604, 606 and 608 in FIG. 6 ) are to be tested for intersectionwith a 3D box 602. FIG. 6 is drawn from the perspective of the origin ofthe rays. The first bundle of rays 604 comprises four rays (shown withthe black circles in FIG. 6 ), and the dashed box represents anaxis-aligned box bounding the bundle of rays 604, i.e. an axis-alignedbox having minimum and maximum component values in each of the x, y andz dimensions equal to the minimum and maximum component values of thedirection vectors of the rays in the bundle. The second bundle of rays606 comprises four rays (shown with the black circles in FIG. 6 ), andthe dashed box represents an axis-aligned box bounding the bundle ofrays 606. The third bundle of rays 608 comprises four rays (shown withthe black circles in FIG. 6 ), and the dashed box represents anaxis-aligned box bounding the bundle of rays 608.

An AllHit test may be performed for the first bundle of rays 604 withrespect to the 3D box 602. The box 602 has six silhouette edges, denoted1 to 6 in FIG. 6 . With respect to silhouette edge 1, components of avector will be obtained which have the maximum y and z values of thedirection vectors of the rays of the bundle 604. In this example, thetop right ray shown in the bundle 604 is an example of a ray havingthese component values in the y and z directions. This vector providesan external bound to the bundle 604 with respect to the silhouette edge1, i.e. if it does not pass outside the identified silhouette point 510₁ then it is known that none of the rays of the bundle 604 pass outsidethe identified silhouette edge 1. It is determined in step S414 that thevector passes inside the silhouette edge 1. In particular, with respectto silhouette edge 1 it is determined in accordance with inequality (11)that (p_(max,z)−o_(z))d_(y)≤(p_(max,y)−o_(y))d_(z), where p_(max,z) isthe z component value of the plane on the top of the box 602, p_(max,y)is the y component value of the plane at the back right of the box 602,o_(y) and o_(z) are the y and z component values of the origin of thebundle of rays 604, and d_(y) and d_(z) are the y and z component valuesof a vector defining the external bound of the bundle 604 with respectto silhouette edge 1. This single test determines that all of the raysof the ray bundle 604 pass inside silhouette edge 1 of the box 602. Withrespect to silhouette edge 6, components of a vector will be obtainedwhich have the minimum x value and the maximum z value of the directionvectors of the rays of the bundle 604. A vector with these x and zcomponents will provide an external bound to the bundle 604 with respectto silhouette edge 6. It is noted that in this example, no one of thefour vectors in the bundle 604 has both the minimum x value and themaximum z value. It is determined in step S414 that a vector with theobtained x and z components passes inside silhouette edge 6. Inparticular, with respect to silhouette edge 6 it is determined inaccordance with inequality (11) that(p_(max,z)−o_(z))d_(x)≤(p_(min,x)−o_(x))d_(z), where p_(max,z) is the zcomponent value of the plane on the top of the box 602, p_(min,x) is thex component value of the plane at the back left of the box 602, o_(x)and o_(z) are the x and z component values of the origin of the bundleof rays 604, and d_(x) and d_(z) are the x and y component values of avector defining the external bound of the bundle 604 with respect tosilhouette edge 6. This single test determines that all of the rays ofthe ray bundle 604 pass inside silhouette edge 6 of the box 602. Forbrevity, we do not describe the tests of bundle 604 with respect tosilhouette edges 2 to 5, but it will be apparent from the description ofthe tests for silhouette edges 1 and 6 and from FIG. 6 that the AllHittest will determine that all of the rays of the bundle 604 are insideall of the silhouette edges of the box 602. Therefore, in step S416, itis determined that the result of the AllHit test for the bundle of rays604 with respect to the box 602 is that all of the rays of the bundle604 hit the box 602.

An AllHit test may be performed for the second bundle of rays 606 withrespect to the 3D box 602. With respect to silhouette edge 2, componentsof a vector will be obtained which have the maximum x and y values ofthe direction vectors of the rays of the bundle 606. In this example,the top right ray shown in the bundle 606 is an example of a ray havingthese component values in the x and y directions. This vector providesan external bound to the bundle 606 with respect to the silhouette edge2. It is determined in step S414 that the vector passes outside thesilhouette edge 2. In particular, with respect to silhouette edge 2inequality (11) is not satisfied, i.e. it is not the case that(p_(max,x)−o_(x))d_(y)≤(p_(max,y)−o_(y))d_(x), where p_(max,x) is the xcomponent value of the plane on the front right of the box 602,p_(max,y) is the y component value of the plane at the back right of thebox 602, o_(x) and o_(y) are the x and y component values of the originof the bundle of rays 606, and d_(x) and d_(y) are the x and y componentvalues of a vector defining the external bound of the bundle 606 withrespect to silhouette edge 2. For brevity, we do not describe the testsof bundle 606 with respect to silhouette edges 1 or 3 to 6, but it willbe apparent from FIG. 6 that the AllHit test will determine that all ofthe rays of the bundle 606 are inside the silhouette edges 3 to 6 of box602, but that not all of the rays of the bundle 606 are insidesilhouette edge 1. Therefore, in step S416, the result of the AllHittest for the bundle of rays 606 with respect to the box 602 is not adetermination that all of the rays of the bundle 606 hit the box 602. Itis noted that in some examples (e.g. implemented in software), the testsmay be performed sequentially for the different silhouette edges, and inthese examples, the result of the AllHit test could be determined assoon as the first “fail” or “miss” result is found for a silhouette edge(e.g. for silhouette edge 1 in the example given above in relation tothe bundle 606), which may avoid having to test one or more othersilhouette edges (e.g. silhouette edges 2-6). However, in other examples(e.g. implemented in hardware) the tests may be performed in parallelfor the different silhouette edges.

Similarly, an AllHit test may be performed for the third bundle of rays608 with respect to the 3D box 602. With respect to silhouette edge 5,components of a vector will be obtained which have the minimum x and yvalues of the direction vectors of the rays of the bundle 608. In thisexample, the bottom left ray shown in the bundle 608 is an example of aray having these component values in the x and y directions. This vectorprovides an external bound to the bundle 608 with respect to thesilhouette edge 5. It is determined in step S414 that the vector passesoutside the silhouette edge 5. In particular, with respect to silhouetteedge 5 inequality (11) is not satisfied, i.e. it is not the case that(p_(min,y)−o_(y))d_(x)≤(p_(min,x)−o_(x))d_(y), where p_(min,x) is the xcomponent value of the plane on the back left of the box 602, p_(min,y)is the y component value of the plane at the front left of the box 602,o_(x) and o_(y) are the x and y component values of the origin of thebundle of rays 608, and d_(x) and d_(y) are the x and y component valuesof a vector defining the external bound of the bundle 608 with respectto silhouette edge 5. For brevity, we do not describe the tests ofbundle 608 with respect to silhouette edges 1 to 4 or 6, but it will beapparent from FIG. 6 that the AllHit test will determine that all of therays of the bundle 608 are inside the silhouette edges 1 to 4 and 6 ofbox 602. Due to the result of the test with respect to silhouette edge5, in step S416, the result of the AllHit test for the bundle of rays608 with respect to the box 602 is not a determination that all of therays of the bundle 608 hit the box 602.

If the result of an AllHit test for a bundle of rays with respect to thebox is not that all of the rays in the bundle of rays intersect the box(e.g. for bundles 506 and 508 with respect to box 502 and for bundles606 and 608 with respect to box 602), then the method may furthercomprise determining whether any of the rays in the bundle of raysintersect the box.

As another example, the bundle intersection test may be an AnyHit test(which may be referred to as an “AllMiss test”, e.g. if the outputs ofthe test were inversed). As described above, there are only two possibleresults from an AnyHit test: either (i) the AnyHit test determines thatall of the rays of the bundle miss the box, or (ii) the AnyHit test doesnot determine that all of the rays of the bundle miss the box. In thisexample, for each of the identified silhouette edges, the vector that isobtained in step S412 provides an internal bound to the bundle of rayswith respect to the identified silhouette edge. The vector provides aninternal bound to the bundle of rays with respect to the identifiedsilhouette edge in the sense that if it does not pass inside theidentified silhouette edge then it is known that none of the rays of thebundle pass inside the identified silhouette edge. As mentioned above,the vector may have either the maximum or the minimum component valuesof the ray direction vectors of the rays in the bundle in eachdimension. Whether the maximum or minimum component value is chosen ineach dimension depends upon the silhouette edge being tested and whetheran internal bound or an external bound is being provided by the vector.The resulting vector may or may not be the same as the direction vectorof one of the rays of the bundle.

If it is determined that, for each of the identified silhouette edges,the respective vector passes inside the identified silhouette edge, thenthe intersection testing result for the bundle of rays with respect tothe box is not that all of the rays in the bundle of rays miss the box.If it is determined that, for one or more of the identified silhouetteedges, the vector passes outside the respective identified silhouetteedge, then the intersection testing result for the bundle of rays withrespect to the box is that all of the rays in the bundle of rays missthe box.

For example, in the 2D example shown in FIG. 5 , an AnyHit test may beperformed for the first bundle of rays 504 with respect to the 2D box502. With respect to silhouette point 510 ₁, the vector 504 ₂ isobtained (in step S412) for the bundle 504 because this vector 504 ₂provides an internal bound to the bundle 504 with respect to thesilhouette point 510 ₁, i.e. if it does not pass inside the identifiedsilhouette point 510 ₁ then it is known that none of the rays of thebundle 504 pass inside the identified silhouette point 510 ₁. It isdetermined in step S414 that the vector 504 ₂ passes inside thesilhouette point 510 ₁. In particular, with respect to silhouette point510 ₁ it is determined in accordance with inequality (11) that(p_(min,x)−o_(x))d_(y,2)≤(p_(max,y)−o_(y))d_(x,2), where p_(min,x) andp_(max,y) are the x and y component values at point 510 ₁, o_(x) ando_(y) are the x and y component values of the origin of the bundle ofrays 504, and d_(x,2) and d_(y,2) are the x and y component values ofthe direction of vector 504 ₂. With respect to silhouette point 510 ₂,the vector 504 ₁ is obtained (in step S412) for the bundle 504 becausethis vector 504 ₁ provides an internal bound to the bundle 504 withrespect to the silhouette point 510 ₂. It is determined in step S414that the vector 504 ₁ passes inside the silhouette point 510 ₂. Inparticular, with respect to silhouette point 510 ₂ it is determined inaccordance with inequality (11) that(p_(min,y)−o_(y))d_(x,1)≤(p_(max,x)−o_(x))d_(y,1), where p_(max,x) andp_(min,y) are the x and y component values at point 510 ₂, o_(x) ando_(y) are the x and y component values of the origin of the bundle ofrays 504, and d_(x,1) and d_(y,1) are the x and y component values ofthe direction of vector 504 ₁. The results of these two tests are usedto determine that not all of the rays of the bundle 504 miss the box502. Therefore, in step S416, the result of the AnyHit test for thebundle of rays 504 with respect to the box 502 is not a determinationthat all of the rays of the bundle 504 miss the box 502, e.g. at leastone of the rays of the bundle 504 may hit the box 502. In other words,the AnyHit test does not guarantee that all of the rays of the bundle504 miss the box 502.

As another example, in the 2D example shown in FIG. 5 , an AnyHit testmay be performed for the second bundle of rays 506 with respect to the2D box 502. With respect to silhouette point 510 ₁, the vector 506 ₂ isobtained (in step S412) for the bundle 506 because this vector 506 ₂provides an internal bound to the bundle 506 with respect to thesilhouette point 510 ₁. It is determined in step S414 that the vector506 ₂ passes inside the silhouette point 510 ₁. In particular, withrespect to silhouette point 510 ₁ it is determined in accordance withinequality (11) that (p_(min,x)−o_(x))d_(y,2)≤(p_(max,y)−o_(y))d_(x,2),where p_(min,x) and p_(max,y) are the x and y component values at point510 ₁, o_(x) and o_(y) are the x and y component values of the origin ofthe bundle of rays 506, and d_(x,2) and d_(y,2) are the x and ycomponent values of the direction of vector 506 ₂. With respect tosilhouette point 510 ₂, the vector 506 ₁ is obtained (in step S412) forthe bundle 506 because this vector 506 ₁ provides an internal bound tothe bundle 506 with respect to the silhouette point 510 ₂. It isdetermined in step S414 that the vector 506 ₁ passes outside thesilhouette point 510 ₂. In particular, with respect to silhouette point510 ₂ it is determined that the bundle of rays 506 does not satisfyinequality (11). In other words, for the bundle of rays 506, it is nottrue that (p_(min,y)−o_(y))d_(x,1)≤(p_(max,x)−o_(x))d_(y,1), wherep_(max,x) and p_(min,y) are the x and y component values at point 510 ₂,o_(x) and o_(y) are the x and y component values of the origin of thebundle of rays 506, and d_(x,1) and d_(y,1) are the x and y componentvalues of the direction of vector 506 ₁. This single test determinesthat all of the rays of the ray bundle 506 pass outside the silhouettepoint 510 ₂ of the box 502. Therefore, in step S416, the result of theAnyHit test for the bundle of rays 506 with respect to the box 502 isthat all of the rays of the bundle 506 miss the box 502.

As another example, in the 2D example shown in FIG. 5 , an AnyHit testmay be performed for the third bundle of rays 508 with respect to the 2Dbox 502. With respect to silhouette point 510 ₁, the vector 508 ₂ isobtained (in step S412) for the bundle 508 because this vector 508 ₂provides an internal bound to the bundle 508 with respect to thesilhouette point 510 ₁. It is determined in step S414 that the vector508 ₂ passes inside the silhouette point 510 ₁. In particular, withrespect to silhouette point 510 ₁ it is determined in accordance withinequality (11) that (p_(min,x)−o_(x))d_(y,2)≤(p_(max,y)−o_(y))d_(x,2),where p_(min,x) and p_(max,y) are the x and y component values at point510 ₁, o_(x) and o_(y) are the x and y component values of the origin ofthe bundle of rays 508, and d_(x,2) and d_(y,2) are the x and ycomponent values of the direction of vector 508 ₂. With respect tosilhouette point 510 ₂, the vector 508 ₁ is obtained (in step S412) forthe bundle 508 because this vector 508 ₁ provides an internal bound tothe bundle 508 with respect to the silhouette point 510 ₂. It isdetermined in step S414 that the vector 508 ₁ passes inside thesilhouette point 510 ₂. In particular, with respect to silhouette point510 ₂ it is determined in accordance with inequality (11) that(p_(min,y)−o_(y))d_(x,1)≤(p_(max,x)−o_(x))d_(y,1), where p_(max,x) andp_(min,y) are the x and y component values at point 510 ₂, o_(x) ando_(y) are the x and y component values of the origin of the bundle ofrays 508, and d_(x,1) and d_(y,1) are the x and y component values ofthe direction of vector 508 ₁. Therefore, in step S416, the result ofthe AnyHit test for the bundle of rays 508 with respect to the box 502is not that all of the rays of the bundle 508 miss the box 502, e.g. atleast one of the rays of the bundle 508 may hit the box 502. In otherwords, the AnyHit test does not guarantee that all of the rays of thebundle 508 miss the box 502.

It can be seen that the result of the AnyHit test is the same forbundles 504 and 508, i.e. it is not confirmed that all of the rays ineither bundle 504 or 508 miss the box 502. This is the case even thoughsome of the rays of bundle 508 do not hit the box 502.

With reference to the 3D example shown in FIG. 6 , an AnyHit test may beperformed for the first bundle of rays 604 with respect to the 3D box602. With respect to silhouette edge 1, components of a vector will beobtained which have the minimum y and z values of the direction vectorsof the rays of the bundle 604. In this example, the bottom left rayshown in the bundle 604 is an example of a ray having these componentvalues in the y and z directions. This vector provides an internal boundto the bundle 604 with respect to the silhouette edge 1. It isdetermined in step S414 that the vector passes inside the silhouetteedge 1. In particular, with respect to silhouette edge 1 it isdetermined in accordance with inequality (11) that(p_(max,x)−o_(z))d_(y)≤(p_(max,y)−o_(y))d_(x), where p_(max,z) is the zcomponent value of the plane on the top of the box 602, p_(max,y) is they component value of the plane at the back right of the box 602, o_(y)and o_(z) are the y and z component values of the origin of the bundleof rays 604, and d_(y) and d_(z) are the y and z component values of avector defining the internal bound of the bundle 604 with respect tosilhouette edge 1. With respect to silhouette edge 6, components of avector will be obtained which have the maximum x value and the minimum zvalue of the direction vectors of the rays of the bundle 604. A vectorwith these x and z components will provide an internal bound to thebundle 604 with respect to silhouette edge 6. It is noted that in thisexample, no one of the four vectors in the bundle 604 has both themaximum x value and the minimum z value. It is determined in step S414that a vector with the obtained x and z components passes insidesilhouette edge 6. In particular, with respect to silhouette edge 6 itis determined in accordance with inequality (11) that(p_(max,z)−o_(z))d_(x)≤(p_(min,x)−o_(x))d_(z), where p_(max,z) is the zcomponent value of the plane on the top of the box 602, p_(min,x) is thex component value of the plane at the back left of the box 602, o_(x)and o_(z) are the x and z component values of the origin of the bundleof rays 604, and d_(x) and d_(z) are the x and y component values of avector defining the internal bound of the bundle 604 with respect tosilhouette edge 6. For brevity, we do not describe the tests of bundle604 with respect to silhouette edges 2 to 5, but it will be apparentfrom the description of the tests for silhouette edges 1 and 6 and fromFIG. 6 that the AnyHit test will determine that the bundle 604 of raysis inside all of the silhouette edges of the box 602. Therefore, in stepS416, the result of the AnyHit test for the bundle of rays 604 withrespect to the box 602 is not a determination that all of the rays ofthe bundle 604 miss the box 602, e.g. one or more of the rays of thebundle 604 may hit the box 602.

An AnyHit test may be performed for the second bundle of rays 606 withrespect to the 3D box 602. With respect to silhouette edge 2, componentsof a vector will be obtained which have the minimum x and y values ofthe direction vectors of the rays of the bundle 606. In this example,the bottom left ray shown in the bundle 606 is an example of a rayhaving these component values in the x and y directions. This vectorprovides an internal bound to the bundle 606 with respect to thesilhouette edge 2. It is determined in step S414 that the vector passesoutside the silhouette edge 2. In particular, with respect to silhouetteedge 2 inequality (11) is not satisfied, i.e. it is not the case that(p_(max,x)−o_(x))d_(y)≤(p_(max,y)−o_(y))d_(x), where p_(max,x) is the xcomponent value of the plane on the front right of the box 602,p_(max,y) is the y component value of the plane at the back right of thebox 602, o_(x) and o_(y) are the x and y component values of the originof the bundle of rays 606, and d_(x) and d_(y) are the x and y componentvalues of a vector defining the internal bound of the bundle 606 withrespect to silhouette edge 2. This single test determines that all ofthe rays of the ray bundle 606 pass outside silhouette edge 2 of the box602. For brevity, we do not describe the tests of bundle 606 withrespect to silhouette edges 1 or 3 to 6, but it will be apparent fromFIG. 6 that the AnyHit test will determine that the bundle 606 is insidethe silhouette edges 1 and 3 to 6 of box 602. Due to the result of thetest with respect to silhouette edge 2, in step S416, the result of theAnyHit test for the bundle of rays 606 with respect to the box 602 is adetermination that all of the rays of the bundle 606 miss the box 602.

An AnyHit test may be performed for the third bundle of rays 608 withrespect to the 3D box 602. With respect to silhouette edge 5, componentsof a vector will be obtained which have the maximum x and y values ofthe direction vectors of the rays of the bundle 608. In this example,the top right ray shown in the bundle 608 is an example of a ray havingthese component values in the x and y directions. This vector providesan internal bound to the bundle 608 with respect to the silhouette edge5. It is determined in step S414 that the vector passes inside thesilhouette edge 5. In particular, with respect to silhouette edge 5inequality (11) is satisfied, i.e. it is the case that(p_(min,y)−o_(y))d_(x)≤(p_(min,x)−o_(x))d_(y), where p_(min,x) is the xcomponent value of the plane on the back left of the box 602, p_(min,y)is the y component value of the plane at the front left of the box 602,o_(x) and o_(y) are the x and y component values of the origin of thebundle of rays 608, and d_(x) and d_(y) are the x and y component valuesof a vector defining the internal bound of the bundle 608 with respectto silhouette edge 5. For brevity, we do not describe the tests ofbundle 608 with respect to silhouette edges 1 to 4 or 6, but it will beapparent from FIG. 6 that the AnyHit test will determine that the bundle608 is inside the silhouette edges 1 to 4 and 6 of box 602. Therefore,in step S416, the result of the AnyHit test for the bundle of rays 608with respect to the box 602 is not a determination that all of the raysof the bundle 608 miss the box 602, e.g. one or more rays of the bundle608 may hit the box 602.

If the intersection testing result of an AnyHit test for a bundle ofrays with respect to a box is not that all of the rays in the bundle ofrays miss the box, then the method may further comprise determiningwhich of the rays in the bundle of rays intersect the box.Alternatively, if the intersection testing result of an AnyHit test fora bundle of rays with respect to a box corresponding to a parent node ina hierarchical acceleration structure is not that all of the rays in thebundle of rays miss the box, then the method may further compriseperforming an AnyHit test on a box corresponding to a child node, i.e. anode which is a child of the parent node in the hierarchicalacceleration structure.

In some examples, in which a hierarchical acceleration structure isbeing traversed, a bundle of rays can be tested against a boxcorresponding to a root node of the acceleration structure using anAnyHit test. If the result of the AnyHit test for the bundle is a “hit”,which may be referred to as a “pass”, (i.e. if the result of the AnyHittest does not indicate that all of the rays in the bundle miss the box)then the bundle can be tested against boxes corresponding to each of thenodes which are children of the node in the acceleration structure forwhich an intersection was found for the bundle. This process continuesdown through levels of the acceleration structure. If the bundle doesnot pass the AnyHit test (i.e. the AnyHit test determines that all ofthe rays of the bundle miss a box) then the bundle is not tested againstboxes corresponding to nodes which are the children of the node forwhich the AnyHit test returned a “miss” or “fail”. If any of the rays ina bundle would hit a box then the whole bundle is pulled down fortesting at the next lower level of the acceleration structure. As thebundle gets deeper in the hierarchical acceleration structure (i.e. asthe bundle is tested against lower levels of the accelerationstructure), the boxes against which the bundle is tested become smaller,and the chance of rays being unnecessarily involved in intersectiontesting against boxes which they miss increases. Therefore, there may bea threshold level in the hierarchical acceleration structure such thatbelow the threshold level, if a bundle passes an AnyHit test at thethreshold level then the bundle will be split up into individual raysfor testing against boxes corresponding to nodes at the level below thethreshold level. The threshold level could be different in differentexamples, and to give two examples, the threshold level could be basedon the node depth in the hierarchical acceleration structure, or basedon the size of the bounding box being tested. If a bundle of rays passesan AnyHit test against a leaf node then the rays of the bundle may besplit up from the bundle and the individual rays may be tested forintersection with the primitive(s) which are pointed to by the pointersof the leaf node. Alternatively, the bundles could be tested forintersection with the primitives which are pointed to by the pointers ofthe leaf node. The system may comprise different testing blocks fortesting rays against primitives rather than for testing rays againstboxes. It is noted that primitives would not normally be rectangular orcuboidal in shape (primitives are often triangular).

In the examples described above, all of the rays of a bundle of rayshave the same origin. This helps to simplify the intersection testingperformed on the bundles of rays. However, if bundles can only includerays which have the same origin, this places a significant restrictionon which rays can be grouped together to form bundles, meaning that somerays might not be able to be grouped together into a bundle. Primaryrays often have the same origin (i.e. corresponding a viewpoint fromwhich the scene is being viewed). However, secondary rays (i.e. raysemitted from an intersection point in the scene) often have differentorigins. Allowing rays which have different origins to be groupedtogether into a bundle may increase the number of rays (particularlysecondary rays) which can be grouped together into bundles. Methods ofgrouping rays together into bundles are described in more detail belowwith reference to FIG. 10 . In some examples, it is not the case thatall of the rays of a bundle of rays have the same origin. For example,the rays within a bundle of rays can have different origins. There maybe a threshold difference to the origins above which rays will not beincluded in the same bundle. In these examples, even though the originsof the rays within a bundle might not all be exactly the same, thedifferences between the origins of the rays in the bundle is not large.This allows intersection testing to be performed for the bundle whilststill providing useful results with respect to the rays of the bundle.

For example, data for a bundle may specify the maximum and minimum rayorigin component values in each dimension of the rays within the bundle.For example, vectors o_(min) and o_(max) may be specified, wherein thex, y and z components of o_(min) are the minimum of the x, y and zcomponent values of the origins of the rays in the bundle, and whereinthe x, y and z components of o_(max) are the maximum of the x, y and zcomponent values of the origins of the rays in the bundle. Whencomputing the distance from the ray origin to a plane representing aside of a box in the intersection testing process, either the distanceto the minimum origin or the maximum origin for the bundle in aparticular dimension is used. The choice of whether to use the minimumor the maximum components of the origins of the rays of the bundle inthe intersection testing depends upon whether an AllHit test or anAnyHit test is being performed.

For example, for an AnyHit test, it is better to err on the side ofproducing a hit result (i.e. a pass, which indicates that it is not thecase that all of the rays in the bundle miss a box) rather than a missresult (i.e. a fail, which indicates that all of the rays in the bundlemiss the box). This is because if an AnyHit test produces a false missresult (i.e. a miss result when actually one or more of the rays of thebundle hits the box) this can cause rendering errors; whereas if anAnyHit test produces a false hit result (i.e. a hit result when actuallyall of the rays of the bundle miss the box) this will not causerendering errors but could reduce the efficiency of the intersectiontesting, e.g. by meaning that further intersection tests areunnecessarily performed. Therefore, the effective size of the box isincreased such that where the origin component values are beingsubtracted from a minimum plane of the box, the maximum origin componentvalue is used, i.e. where a value of (p_(min,i)−o_(i)) is used in theexamples given above this would be replaced by a value of(p_(min,i)−o_(max,i)) for i∈{x, y, z} where o_(max,i) is the maximum ofthe i^(th) components of the origins of the rays of the bundle.Furthermore, to increase the effective size of the box, where the origincomponent values are being subtracted from a maximum plane of the box,the minimum origin component value is used, i.e. where a value of(p_(max,i)−o_(i)) is used in the examples given above this would bereplaced by a value of (p_(max,i)−o_(min,i)) for i∈{x, y, z} whereo_(min,i) is the minimum of the i^(th) components of the origins of therays of the bundle.

For example, for an AllHit test, it may be better to err on the side ofproducing a miss result (i.e. fail, which indicates that it is not thecase that all of the rays in the bundle hit a box) rather than a hitresult (i.e. a pass, which indicates that all of the rays in the bundlehit the box). This is because if an AllHit test produces a false hitresult (i.e. a hit result when actually one or more of the rays of thebundle misses the box) this may cause a significant decrease in theefficiency of the intersection testing; whereas if an AllHit testproduces a false miss result (i.e. a miss result when actually all ofthe rays of the bundle hit the box) this may produce a less significantdecrease in the efficiency of the intersection testing. Therefore, theeffective size of the box may be decreased such that where the origincomponent values are being subtracted from a minimum plane of the box,the minimum origin component value is used, i.e. where a value of(p_(min,i)−o_(i)) is used in the examples given above this may bereplaced by a value of (p_(min,i)−o_(min,i)) for i∈{x, y, z} whereo_(min,i) is the minimum of the i^(th) components of the origins of therays of the bundle. Furthermore, to decrease the effective size of thebox, where the origin component values are being subtracted from amaximum plane of the box, the maximum origin component value is used,i.e. where a value of (p_(max,i)−o_(i)) is used in the examples givenabove this would be replaced by a value of (p_(max,i)−o_(max,i)) fori∈{x, y, z} where o_(max,i) is the maximum of the i^(th) components ofthe origins of the rays of the bundle.

FIGS. 16 a to 16 c illustrate how the effective size of a box can beincreased or decreased based on the differences in origin values of therays in a bundle. For ease of illustration, the examples shown in FIGS.16 a to 16 c is a 2D example, but it will be apparent how the effectivesize of a box can be increased or decreases in a 3D example too. FIG. 16a shows a box 1602 with the minimum position vector p_(min) and themaximum position vector p_(max) being shown. In this example, the bundleof rays includes four rays, which have origins at the positions shown bythe solid black circles in FIG. 16 a . The axis aligned bounding box1604 bounds all of the origins. The bounding box 1604 has a maximumposition vector o_(max) and a minimum position vector o_(min) as shownin FIG. 16 a . Distances between p_(min) and o_(max) and o_(min) in thex and y directions are illustrated in FIG. 16 a.

FIG. 16 b illustrates how, in the example of an AnyHit test, theeffective size of the box 1602 can be increased based on the differencesin the origin values of the rays in the bundle. The bundle of rays canbe treated as if it had a single origin at position o. The effectivesize of the box 1602 is increased to be the box 1606 as shown with thedashed lines in FIG. 16 b . The minimum position vector of the effectivebox 1606 is at a position [p_(min)−(o_(max)−o)], and the maximumposition vector of the effective box 1606 is at a position[p_(max)−(o_(min)−o)]. The distance to the minimum vector position ofthe effective box 1606, in the x dimension, is given by[p_(min,x)−(o_(max,x)−o_(x))]−o_(x) which is the same as[p_(min,x)−o_(max,x)] illustrated in FIG. 16 a ; and the distance to theminimum vector position of the effective box 1606, in the y dimension,is given by [p_(min,y)−(o_(max,y)−o_(y))]o_(y) which is the same as[p_(min,y)−o_(max,y)] illustrated in FIG. 16 a . Similarly calculationscan be made for determining the distance between the bundle of rays andthe maximum vector position of the effective box 1606. It can beappreciated that, in the AnyHit example, increasing the effective sizeof the box 1602 to be the box 1606 and using a single origin value isequivalent to treating the bundle of rays as having different originvalues to be tested against the original box 1602.

FIG. 16 c illustrates how, in the example of an AllHit test, theeffective size of the box 1602 can be decreased based on the differencesin the origin values of the rays in the bundle. In particular, theeffective size of the box 1602 is decreased to be the box 1608 as shownwith the dashed lines in FIG. 16 c . The minimum position vector of theeffective box 1608 is at a position [p_(min)−(o_(min)−o)], and themaximum position vector of the effective box 1608 is at a position[p_(max)−(o_(max)−o)]. The bundle of rays can be treated as if it had asingle origin at position o, and the distance to the minimum vectorposition of the effective box 1608, in the x dimension, is given by[p_(min,x)−(o_(min,x)−o_(x))]−o_(x) which is the same as[p_(min,x)−o_(min,x)] illustrated in FIG. 16 a ; and the distance to theminimum vector position of the effective box 1608, in the y dimension,is given by [p_(min,y)−(o_(min,y)−o_(y))]−o_(y) which is the same as[p_(min,y)−o_(min,y)] illustrated in FIG. 16 a . Similarly calculationscan be made for determining the distance between the bundle of rays andthe maximum vector position of the effective box 1608. It can beappreciated that, in the AllHit example, decreasing the effective sizeof the box 1602 to be the box 1608 and using a single origin value isequivalent to treating the bundle of rays as having different originvalues to be tested against the original box 1602.

Therefore, if the rays in a bundle do not all have the same origin, foreach of the identified silhouette edges, step S414 of determiningwhether the vector passes inside or outside of the silhouette edgecomprises performing a comparison in accordance with(p_(o,i)−o_(i,[min,max]))d_(j)<(p_(o,j)−o_(j,[min,max]))d_(i), whereinp_(o,i) is the i^(th) component of a point on a first plane representinga first of the sides of the box which forms the silhouette edge, p_(o,j)is the j^(th) component of a point on a second plane representing asecond of the sides of the box which forms the silhouette edge,o_(i[min,max]) is either the minimum or the maximum of the i^(th)components of the origins of the rays of the bundle of rays,o_(j[min,max]) is either the minimum or the maximum of the j^(th)components of the origins of the rays of the bundle of rays, and d_(i)and d_(j) are the obtained i^(th) and j^(th) components of the vectorproviding a bound to the bundle of rays.

In the examples described above and shown in FIGS. 5 and 6 , thedirection vectors of the rays in a bundle all have the same sign. Inthese examples, the silhouette edges of the box are at opposing edges ofthe box. However, if the direction vectors of the rays in a bundle donot all have the same sign for one or more of their component values,then the step of identifying the silhouette edges (step S410) mayidentify different edges of the box. For example, FIG. 7 shows a 2Dexample in which a bundle of rays 704 is to be tested for intersectionwith the 2D box 702. The two bounding vectors 704 ₁ and 704 ₂ for thebundle 704 have different signs in their x component values, but their ycomponent values have the same sign. In some examples, the rays aregrouped into ray bundles with the requirement that, in each dimension,the component values of the bounding vectors have the same signs, but inother examples this is not a requirement for grouping rays together intoa bundle. As shown in FIG. 7 , in this example, the silhouette points ofthe 2D box 702 are 710 ₁ and 710 ₂. These two silhouette points both lieon the edge of the box 702 that is closest to the origin of the bundleof rays 704. Therefore, the silhouette points 710 ₁ and 710 ₂ are not atdiametrically opposed corners of the box 702. As an example, an AllHittest performed on the bundle 704 with respect to the box 702 willdetermine that all of the rays of the bundle 704 hit the box 702 becausevector 704 ₁ passes inside silhouette point 710 ₁ and because vector 704₂ passes inside silhouette point 710 ₂. It is apparent from FIG. 7 thatif diametrically opposed points of the box 702 were used as thesilhouette points of the box then an AllHit test performed on the bundle704 with respect to the box 702 would not determine that all of the raysof the bundle 704 hit the box 702.

FIG. 8 a shows a 3D example in which, due to the perspective from whicha box 802 is being viewed the silhouette edges (denoted 1 to 6 in FIG. 8a ) are not all in diametrically opposed pairs. For example, the edgesdiametrically opposed to silhouette edges 2, 3, 5 and 6 are notsilhouette edges of the box 802 when viewed from the perspective shownin FIG. 8 a . FIG. 8 b shows a 3D example in which, due to theperspective from which a box 804 is being viewed there are only foursilhouette edges (denoted 1 to 4 in FIG. 8 b ) which are notdiametrically opposed edges of the box 804. It is noted that the box 804is a 3D box, but from the perspective shown in FIG. 8 b only one side ofthe box 804 can be seen such that the edges of this one side of the box804 are the silhouette edges of the 3D box 804 when viewed from theperspective shown in FIG. 8 b.

FIG. 9 shows another example ray tracing system 900 for performingintersection testing in the manner described above. Ray tracing system900 is similar to ray tracing system 300 in that it comprises ascheduler 901, request queue 903, memory 905 and a tester module 907,and in that the tester module 907 comprises a test queue 909 and aresults processor 913. The tester module 907 also comprises a set of oneor more first testing blocks (configured to perform AllHit bundleintersection tests), and a set of one or more second testing blocks(configured to perform AnyHit bundle intersection tests). The testingblocks are organised into pairs of testing blocks, each pair of testingblocks comprising: (i) one first testing block from the set of one ormore first testing blocks, and (ii) one second testing block from theset of one or more second testing blocks. For example, FIG. 9 shows afirst pair of testing blocks comprising an AllHit testing block 915 ₁and an AnyHit testing block 915 ₂; and a second pair of testing blockscomprising an AllHit testing block 917 ₁ and an AnyHit testing block 917₂. The results processor 913 is configured to process the intersectiontesting results determined by the testing blocks.

The ray tracing system 900 also comprises a bundle builder (e.g.implemented in hardware or software, or a combination thereof) which isconfigured to receive rays and construct bundles of rays from thereceived rays to be tested for intersection with a box. The bundles maybe constructed by grouping rays together based on their similarity. Theterm “similarity” used here refers to whether rays have similar originsand directions. That is, rays that have similar origins and similardirections are “similar” rays. The bundle builder groups similar raysinto bundles so that bundle intersection tests can be performed on thebundles. Furthermore, it is noted that the scheduler 901 groups coherentrays and/or bundles into packets. Here the term “coherent” means thatthe rays and/or bundles will access the same memory location forretrieving nodes to be tested against for intersection. “Similar” rayswhich are grouped into a bundle are also “coherent” rays because thesesimilar rays will access the same memory location for intersectiontesting. However, “coherent” rays are not necessarily “similar”. Inother words, some rays which will access the same memory location forretrieving nodes to be tested against for intersection might not havesimilar origins and directions. The way in which the bundle builder 919groups rays into bundles may be controlled by a similarity threshold,e.g. by allowing new rays to merge with a bundle if the solid anglerepresenting the bounding vectors of the bundle is kept below athreshold, and/or as another example, by keeping the bounding box of theorigins of the rays within a bundle below a certain size. This sizethreshold could be relative to the size of the scene. Alternatively, asimpler direction threshold would be to say, for each of the icomponents, the range of the i^(th) component values for the directionvectors of the rays in a bundle has a maximum value. In other words, avalue of d_(max,i)−d_(min,i) for each of the i components, has a maximumvalue. In this example, the direction vectors are normalised so thatthey are comparable.

FIG. 10 shows a flow chart for a method performed by the ray tracingsystem 900. In step S1002, the bundle builder 919 receives rays to betested for intersection with one or more boxes. The bundle builder 919may maintain a set of open bundles to which the received rays can beadded. The bundle builder 919 may have some local memory in order tostore the open bundles. Steps S1006 to S1016 are performed for each ofthe received rays. In step S1006, the bundle builder 919 determines alevel of similarity of a received ray with each of the open bundles.This can be done by, for each of the open bundles, seeing how much, ifat all, the bundle bounds were to grow if the ray was added to thebundle. For example, if the origin of the ray is outside the boundingbox of the origins for a bundle, then a similarity determination couldbe made based on a distance between the origin of the ray and thebounding box of the origins for the bundle, and whether this distance isbelow a threshold. If the direction vector of the ray has componentswhich are larger than the maximum direction of the bundle or smallerthan the minimum direction of the bundle, then a similaritydetermination could be made based on a difference between the directionvector of the ray and the minimum or maximum direction of the bundle,and whether this difference is below a threshold. These thresholds couldbe fixed or they could be percent-increase based thresholds, e.g. basedon a percentage increase in the bounding box for the origins of thebundle or based on a percentage increase in the difference between themaximum and minimum direction vectors for the bundle if the ray were tobe added to the bundle. In step S1008 the bundle builder 919 identifiesa best match open bundle of said set of open bundles for the receivedray based on the determined levels of similarity. For example, the openbundle which has the highest level of similarity with the ray may beidentified in step S1008.

In step S1010 the bundle builder 919 determines whether the level ofsimilarity of the ray with the best match open bundle is above athreshold level of similarity. In other words, the bundle builder 919determines whether the ray is sufficiently similar to the best matchopen bundle for the ray to be added to the best match open bundle. If itis determined in step S1010 that the determined level of similarity ofthe received ray with the best match open bundle is above the threshold,then the method passes to step S1012 in which the received ray is addedto the best match open bundle. If it is determined in step S1010 thatthe determined level of similarity for the best match open bundle isbelow the threshold, then the method passes to step S1014 in which a newbundle is created, i.e. a new open bundle is created which initiallycomprises no rays but to which rays can be added. As part of step S1014,if there is no space to create a new open bundle then an existing bundlemay be selected and outputted from the bundle builder 919 and passed tothe scheduler 901, in order to make space to create the new open bundle.Then in step S1016 the received ray is added to the new bundle.

In step S1018 bundles which are full (i.e. bundles which are ready to betested for intersection with a box) are outputted from the bundlebuilder 919 and passed to the scheduler 901.

The scheduler 901 operates in a similar manner to the scheduler 301described above. However, the scheduler 901 can form packets comprisingpointers to rays and/or bundles of rays. It does not make a differenceto the grouping of the pointers into packets whether the pointers arefor individual rays or for bundles of rays. In other words, rays andbundles can be mixed within a packet, and a packet can contain multipleof each (i.e. pointers to multiple rays and to multiple ray bundles).The scheduler 901 groups, into packets, rays and/or bundles of rayswhich require access to the same block of memory 905. In other words, instep S1020, the scheduler 901 forms packets comprising one or both ofindications of rays and indications of bundles of rays which willrequire access to the same block of memory for performing intersectiontesting. For example, rays and/or bundles which are to be tested withrespect to the same box or object may be grouped into a packet, suchthat the data for the box or object can be fetched once from the memory905 for use in the intersection testing of all of the rays and/orbundles in the packet. Once the scheduler has assembled the rays and/orbundles into a packet, the scheduler will issue the packet and cause thepacket to join the request queue 903 to request the node data for thepacket (i.e. data describing a box corresponding to the appropriate nodeof the acceleration structure against which the rays and/or bundles ofthe packet are to be tested for intersection) from memory 905. In stepS1022 the node data for the packet is then retrieved from memory 905. Inother words, in step S1022, data is fetched from the block of memory forperforming intersection testing on the one or both of rays and bundlesof rays indicated by the indications in the packet. In step S1024 thefetched data is passed to the tester module 307, so that the testermodule 307 can perform intersection testing as described herein, e.g.with reference to the flow charts of FIG. 4, 11 or 12 .

In a first example, there may be persistent root bundles. In thisexample, once a ray has been added to a bundle, it will not be separatedfrom that bundle and grouped together into a different bundle. In otherwords, the bundle builder 919 only processes new rays in this example,i.e. primary rays and freshly spawned secondary rays. In this example,results output from the results processor 913 can go directly to thescheduler 901, or they could go to the bundle builder 919 which couldthen simply forward the results to the scheduler 901. FIG. 9 shows theoutput from the results processor 913 with a dashed line because indifferent implementations this output could go to either the bundlebuilder 919 or the scheduler 901. In this example, once a bundle hasstarted traversal it can be broken down (e.g. split up into individualrays), but the rays within the bundle cannot be recombined or reformedinto other bundles. In other words, the rays from which the bundles areconstructed: (i) include new rays which have not previously beenincluded in a bundle of rays, but (ii) do not include rays which havepreviously been included in a bundle of rays. In this example, since thebundle builder 919 only processes new rays it only needs to run fastenough to process a relatively small number of rays (e.g. one or tworays) each cycle. Furthermore, data for individual rays inside a bundledoes not need to accessed on every iteration (e.g. to start eachintersection test at each level of the acceleration structure) andinstead just needs to be accessed when the bundle collapses, e.g. whenthe individual rays are split from the bundle. This allows the data forthe bounding vectors of the bundle to be stored separately to the raydata of the individual rays, so the amount of data needed to perform abundle intersection test is comparable (i.e. similar, e.g. approximatelyequal to) the amount of data needed to perform a ray intersection teston a single ray.

In a second example, bundles may be reformed. In this example, bundleswould be broken down and reconstructed after every iteration ofintersection tests (e.g. after each bundle intersection test). In thisexample, the tester module 907 would be modified to deconstruct bundlesinto individual rays and pass results for individual rays to the bundlebuilder 919. The bundle builder would be responsible for forming bundlesas ray results arrive, and outputting the bundles to the scheduler 901.In some examples, the scheduler 901 could receive the results from theresults processor 913 and form the bundles. Since the scheduler 901handles coherence gathering for grouping rays and/or bundles intopackets, it is not a major modification to have the scheduler 901 alsoform bundles of similar rays (noting that similar rays are coherent). Inthese examples, the rays from which the bundles are constructed include:new rays which have not previously been included in a bundle of rays,and rays which have previously been included in a bundle of rays whichhas been deconstructed. In these examples, bundles can be merged withother bundles or rays during traversal of an acceleration structure,which may provide more opportunities for getting the benefit fromperforming the bundle intersection tests (e.g. because bundles mayinclude, on average, a larger number of rays, or because, on average,the similarity of the rays within a bundle may be increased (compared tothe first example described in the preceding paragraph in whichpersistent root bundles are implemented)). However, in this secondexample, extra logic (e.g. extra hardware) would be required to formbundles for many rays per clock (where the number of rays per clockwould be dependent upon the number of testing blocks in the testermodule 907). This second example also requires reading of all the raydata for a packet on each iteration, which is not required in the firstexample described in the preceding paragraph.

The testing blocks described above (which may be configured to performeither an AllHit test or an AnyHit test on a bundle of rays) are alsoconfigured to perform intersection testing for a single ray. In otherwords, these testing blocks can be used as individual ray testers, e.g.for performing intersection testing for a ray with respect to a box. Asingle ray may be considered to be a bundle comprising a single ray. Fora bundle comprising a single ray, the bounding vectors of the bundlewould just be the direction vector of the single ray and the maximum andminimum components of the origin of the bundle would just be thecomponents of the origin of the ray. In this situation, both the AllHittest and the AnyHit test described above would give the correctintersection testing results for the single ray in the bundle. This isuseful because the ray tracing systems 300 and 900 do not need dedicatedsingle ray testing blocks and dedicated bundle testing blocks: the sametesting blocks can be used for performing both bundle intersectiontesting and single ray intersection testing. This reduces the likelihoodof bottlenecking due to one type of testing block being saturated whilstanother type of testing block is idle.

The tester module 907 comprises a memory 921 configured to store datadescribing a box which has been fetched from the memory 905 forperforming the intersection testing with respect to the box. Forexample, the data for the box can be fetched from the memory 905 andstored in the local memory 921 when a bundle is to be tested forintersection with respect to the box. If the bundle collapses, i.e. ifthe rays in the bundle are split up into individual rays, the data forthe individual rays can be fetched from the memory 905 (or from someother memory, e.g. an on-chip memory (e.g. part of the local memory 921)used for storing ray data close to the testing blocks) and tested forintersection with respect to the box using the data for the box that isstored in the local memory 921. The local memory 921 temporarily storesdata for the box when it is fetched from the memory 905 so this data canbe reused, e.g. when a bundle collapses, without taking a round-tripthrough memory 905, i.e. without re-fetching the data for the box fromthe memory 905.

AllHit tests and AnyHit tests have been described above, and each ofthese two types of bundle intersection tests may be performedseparately, each providing a benefit, e.g. a reduction in the totalnumber of intersection tests that need to be performed. However, in someexamples, both AllHit and AnyHit tests may be performed. For example,FIG. 11 shows a flow chart for a method of performing intersectiontesting at the ray tracing system 900.

In step S1102, the tester module 907 receives a bundle of rays to betested for intersection with a box. In step S1104 a first testing block(e.g. testing block 915 ₁ or 917 ₁) performs a first bundle intersectiontest (i.e. an AllHit test) to determine whether or not all of the raysof the bundle intersect the box. As described above, the AllHit test hastwo possible outcomes: either (i) it is determined that all of the raysof the bundle hit the box, or (ii) it is not determined that all of therays of the bundle hit the box. The result of the first bundleintersection test is considered in step S1106. If the first bundleintersection test determines that all of the rays of the bundle hit thebox then the method passes from step S1106 to step S1108. In step S1108it is determined that an intersection testing result for the bundle withrespect to the box is that all of the rays of the bundle intersect thebox.

If the first bundle intersection test does not determine that all of therays of the bundle hit the box then the method passes from step S1106 tostep S1110. In step S1110 a second testing block (e.g. testing block 915₂ or 917 ₂) performs a second bundle intersection test (i.e. an AnyHittest) to determine whether or not all of the rays of the bundle miss thebox. As described above, the AnyHit test has two possible outcomes:either (i) it is determined that all of the rays of the bundle miss thebox, or (ii) it is not determined that all of the rays of the bundlemiss the box. The result of the second bundle intersection test isconsidered in step S1112. If the second bundle intersection testdetermines that all of the rays of the bundle miss the box then themethod passes from step S1112 to step S1114. In step S1114 it isdetermined that the intersection testing result for the bundle withrespect to the box is that all of the rays of the bundle miss the box.

If the second bundle intersection test does not determine that all ofthe rays of the bundle miss the box then the method passes from stepS1112 to step S1116. Therefore, the method reaches step S1116 if thefirst bundle intersection test does not determine that all of the raysof the bundle intersect the box and if the second bundle intersectiontest does not determine that all of the rays of the bundle miss the box.In step S1116 the bundle of rays is split up into individual rays. Forexample, the results processor 913 can split up a bundle of rays intoindividual rays. Then in step S1118 intersection tests are performed forthe individual rays with respect to the box to determine which of theindividual rays intersect the box. Intersection testing may be performedon the individual rays by one or more of the testing blocks withoutfirst passing the individual rays back to the bundle builder 919 or thescheduler 901. After intersection testing has been performed on theindividual rays, the results of the intersection testing for theindividual rays may be output from the tester module 907 (e.g. from theresults processor 913). If the intersection testing finds a hit for anindividual ray then that ray can be processed as if it is a newlyreceived ray to be tested against the boxes represented by the childnodes of the node representing the box that it has just been found tointersect. For example, the individual rays for which hits have beenfound may be output from the results processor 913 to the bundle builder919 or the scheduler 901 so that the individual rays can be grouped intobundles and/or packets and passed to the request queue 903, so that theycan be processed as if they were newly received rays to be testedagainst the boxes represented by the child nodes of the noderepresenting the box that they have just been found to intersect. Asmentioned above, data for the box may be stored in the local memory 921and the same testing blocks (e.g. 915 ₁, 915 ₂, 917 ₁ and 917 ₂) may beused to perform the intersection tests for the individual rays withrespect to the box.

In the method shown in the flow chart of FIG. 11 the second bundleintersection testing (e.g. the AnyHit testing) is performedconditionally based on the result of the first bundle intersectiontesting (e.g. the All Hit testing). In other words, in this example, theAnyHit testing is performed for a bundle with respect to a box inresponse to the result of the AllHit test not being a determination thatall of the rays of the bundle hit the box. This is an example of how themethod could be implemented in software, e.g. if the testing blocks inthe tester module 907 are implemented as blocks of software code whichcan be executed on a processing unit.

FIG. 12 shows a flow chart for another method of performing intersectiontesting at the ray tracing system 900. The flow chart may be moresuitable for being implemented in hardware, e.g. if the testing blocksin the tester module 907 are hardware blocks (e.g. implemented in fixedfunction circuitry) configured to perform intersection testing. In themethod shown in FIG. 12 the first bundle intersection testing (e.g.AllHit testing) and the second bundle intersection testing (e.g. AnyHittesting) are both performed for a bundle of rays with respect to a boxunconditionally, i.e. without dependence upon the result of the otherbundle intersection testing for the bundle of rays with respect to thebox. In particular, the second bundle intersection testing (e.g. AnyHittesting) is performed irrespective of the result of the first bundleintersection testing (e.g. AllHit testing).

In step S1202, the tester module 907 receives a bundle of rays to betested for intersection with a box. Following step S1202, steps S1204and S1210 are performed in parallel. In step S1204 a first testing block(e.g. testing block 915 ₁ or 917 ₁) performs a first bundle intersectiontest (i.e. an AllHit test) to determine whether or not all of the raysof the bundle intersect the box. The result of the first bundleintersection test is considered in step S1206. If the first bundleintersection test determines that all of the rays of the bundle hit thebox then the method passes from step S1206 to step S1208. In step S1208it is determined that an intersection testing result for the bundle withrespect to the box is that all of the rays of the bundle intersect thebox. If the first bundle intersection test does not determine that allof the rays of the bundle hit the box then the method passes from stepS1206 to step S1215.

In step S1210 a second testing block (e.g. testing block 915 ₂ or 917 ₂)performs a second bundle intersection test (i.e. an AnyHit test) todetermine whether or not all of the rays of the bundle miss the box. Theresult of the second bundle intersection test is considered in stepS1212. If the second bundle intersection test determines that all of therays of the bundle miss the box then the method passes from step S1212to step S1214. In step S1214 it is determined that the intersectiontesting result for the bundle with respect to the box is that all of therays of the bundle miss the box. If the second bundle intersection testdoes not determine that all of the rays of the bundle miss the box thenthe method passes from step S1212 to step S1215.

The results from both the first testing block and the second testingblock are passed to the results processor 913. In step S1215 the resultsprocessor 913 determines whether the results of both steps S1206 andS1212 are ‘No’. In other words, the results processor 913 determineswhether both: (i) the AllHit test does not determine that all of therays of the bundle hit the box, and (ii) the AnyHit test does notdetermine that all of the rays of the bundle miss the box. If this isthe case, the method passes from step S1215 to step S1216. In step S1216the results processor 913 splits up the bundle of rays into individualrays. Then in step S1218 intersection tests are performed for theindividual rays with respect to the box to determine which of theindividual rays intersect the box. The individual rays (or references tothe individual rays, e.g. ray IDs) may be output from the resultsprocessor back to one or more of the testing blocks for performing theintersection testing on the individual rays. Alternatively, theindividual rays may be output from the results processor 913 andprocessed as if they were newly received rays. For example, theindividual rays may be output from the results processor 913 to thebundle builder 919 or the scheduler 901 so that the individual rays canbe grouped into bundles and/or packets and passed to the request queue903, so that they can be processed as if they were newly received rays.As mentioned above, data for the box may be stored in the local memory921 and the same testing blocks (e.g. 915 ₁, 915 ₂, 917 ₁ and 917 ₂) maybe used to perform the intersection tests for the individual rays withrespect to the box.

In some examples, the ray data for the rays can be stored in an on-chipmemory (as part of the local memory 921), and each ray has an identifier(which may be referred to as a “RayID”). Where we describe passing“rays” between blocks, in some examples, this can be implemented bypassing RayIDs between the blocks, such that the actual ray data for therays (e.g. the ray origin and direction etc.) does not need to be passedbetween the blocks. A testing block (e.g. 915 or 917) can read the raydata indicated by a RayID just before it is to perform an intersectionon the ray, e.g. by fetching the ray data from the local memory. Inexamples in which bundles are recreated, the ray data may be pipelinedfrom the tester module 907 to the bundle builder 919 so it has ray datafor creating the bundles.

The structure of the packets created by the scheduler 901 may be anindication of a location of data in memory and a list, e.g. a linkedlist, of blocks of RayIDs. The scheduler 901 builds up the lists ofRayIDs for each packet it is creating. Each of the bundles could haveits own RayID, and a pointer to a list of RayIDs for each ray in thebundle. If a bundle is to be collapsed (i.e. split up into individualrays), the results processor 913 may pass the pointers for theindividual rays back to the frontend of the tester module 907. Inessence, the packet for individual rays has been created a priori by theresults processor 913 in this case. The testing blocks of the testermodule 907 read the ray data for the individual rays right before eachintersection test as normal.

In general, packets contain references to rays, and the ray data isfetched by the tester module when it is to be used for intersectiontesting.

If in step S1215 the results processor 913 determines that the result ofeither step S1206 or step S1212 is Yes' (in other words, if the resultsprocessor 913 determines that: (i) the AllHit test determines that allof the rays of the bundle hit the box, or (ii) the AnyHit testdetermines that all of the rays of the bundle miss the box) then themethod performed by the testing blocks ends after step S1215 because anintersection testing result has been already been determined for thebundle with respect to the box. In other words either the AllHit test orthe AnyHit test has determined the intersection testing result for thebundle with respect to the box and this result has been output to theresults processor 913, so there is no need to split up the bundle intoindividual rays in order to determine the intersection testing resultfor all of the rays of the bundle with respect to the box.

In both of the examples shown in FIGS. 11 and 12 , if the first bundleintersection test (e.g. the AllHit test) does not determine that all ofthe rays of the bundle intersect the box, a result of performing thesecond bundle intersection test (e.g. the AnyHit test) is used todetermine the intersection testing result for the bundle with respect tothe box. The main difference between the two methods is that in themethod of FIG. 11 , the second bundle intersection test is performedconditionally based on the result of the first bundle intersection test;whereas in the method of FIG. 12 , the first and second bundleintersection tests are performed concurrently, in parallel. In otherwords, in the method of FIG. 12 , the second bundle intersection test(e.g. the AnyHit test) is performed irrespective of the result of thefirst bundle intersection test (e.g. the AllHit test).

In some other examples, which are not described in detail herein, itwould be possible to perform the first bundle intersection test (e.g.the AllHit test) conditionally based on the result of the second bundleintersection test (e.g. the AnyHit test). In these other examples, ifthe AnyHit test determined that all of the rays of the bundle miss thebox then the AllHit test would not be performed, whereas if the resultof the AnyHit test is not a determination that all of the rays of thebundle miss the box then the AllHit test would be performed.

As described above, the tester module 907 of the ray tracing system 900comprises pairs of testing blocks wherein each pair of testing blockscomprises an AllHit testing block and an AnyHit testing block. Thetester module 907 is configured to pass a bundle of rays and datarepresenting a box to a pair of testing blocks (e.g. testing blocks 915₁ and 915 ₂), such that the first testing block 915 ₁ of the pair oftesting blocks performs the first bundle intersection test (e.g. theAllHit test) on the bundle of rays with respect to the box, and thesecond testing block 915 ₂ of the pair of testing blocks performs thesecond bundle intersection test (e.g. the AnyHit test) on the bundle ofrays with respect to the box. In this way, when intersection testing isbeing performed for a bundle of rays, the bundle is passed to bothtesting blocks of a pair of testing blocks for intersection testing.

As described above, the testing blocks can also be used to performintersection tests for individual rays. The tester module 907 isconfigured to pass first and second individual rays and datarepresenting a box to a pair of testing blocks (e.g. testing blocks 915₁ and 915 ₂), such that the first testing block 915 ₁ of the pair oftesting blocks performs an intersection test on the first individual raywith respect to the box, and the second testing block 915 ₂ of the pairof testing blocks performs an intersection test on the second individualray with respect to the box. In this way, when intersection testing isbeing performed for individual rays, two individual rays can be passedto the respective testing blocks of a pair of testing blocks forintersection testing. It can therefore be appreciated that in someexamples, a bundle of rays will occupy a pair of testing blocks at atime, while single rays only occupy one testing block at a time.

FIG. 13 a shows an example data structure for storing data for a ray. Inthis example, each ray has 64 bytes of data. As shown in FIG. 13 a , theray data for a ray includes x, y and z components of the origin of theray; x, y and z components of the direction vector of the ray; x and ycomponents (“PosX” and “PosY”) to indicate a screen space position withwhich the ray is associated, which can be used to write back a result; amaximum distance that the ray can travel (“MaxT”); a distance to anearest hit (“T”); barycentric U and V components of a hit point on aprimitive; an ID of a shader on a hit primitive (“hit ID”); one or moreflags which can be used to implement various per-ray API features, suchas backface culling; and user data which can be written to, e.g. byshader programs.

The data for a bundle of rays is stored in a data structure andcomprises origin data for the bundle of rays; vector data describing thecomponents of the vectors providing the bounds to the bundle of rays;and one or more pointers to ray data for the rays of the bundle of rays.For example, FIG. 13 b shows a data structure for storing data for abundle of rays. In this example, each bundle of rays has 64 bytes ofdata. In the example shown in FIG. 13 b , each row represents a valuehaving 32 bits of data. Having the same size data structures for raydata and for bundle data is convenient because it allows bundles andrays to be packed together into packets easily. As shown in FIG. 13 b ,the data for a bundle of rays includes minimum and maximum x, y and zcomponents of the origin of the bundle of rays; minimum and maximum x, yand z components of the bounding vectors of the bundle of rays; amaximum distance that the bundle of rays can travel (“MaxT”); a distanceto a nearest hit (“T”); one or more flags which can be used to implementvarious per-ray API features, such as backface culling; and one or moreray pointers which indicate data for the rays of the bundle. Forexample, a ray pointer could point to another packet of data whichcontains all of the ray data for the rays which make up the bundle. Thisray pointer would be followed once per bundle, when the bundle is brokendown into individual rays. For example, the results processor 913 canpass this pointer back to the test queue 909, and it gets treated thesame as when a pointer to a list of rays comes from the scheduler path(e.g. from the request queue 903).

In some examples, a bundle of rays may be split up into individual raysif a splitting metric is satisfied. For example, the splitting metricmay be based on one or more of: a number of rays in the bundle of rays;a spread of the rays in the bundle of rays; a size of an area defined bythe silhouette edges of the box; whether the source of the rays in thebundle of rays is a frame shader or a ray shader; and data provided bythe shader which created the rays in the bundle of rays (e.g.information relating to how diffuse a ray is). For example, if thenumber of rays in a bundle is below a threshold then the bundle may bedeconstructed, i.e. split up into individual rays. The benefit providedby performing bundle intersection testing rather than individual rayintersection testing is not so large if there are not so many rays inthe bundle. For example, if there are only two rays in a bundle, it maybe better to split the rays up and test them individually rather thanperforming bundle intersection tests. As another example, if the spreadof rays in a bundle is above a threshold then it may be considered thatthe rays are too divergent and the bundle may be split up. In this case,if the spread of the rays in a bundle is too large then the rays areless likely to have the same intersection testing results, so performingthe bundle intersection tests is less beneficial. The larger the spreadof the rays in a bundle, the bigger the difference between the maximumand minimum bounding vector components for the bundle.

FIG. 14 shows a computer system in which the ray tracing systemsdescribed herein may be implemented. The computer system comprises a CPU1402, a GPU 1404, a memory 1406 and other devices 1410, such as adisplay 1412, speakers 1414 and a camera 1416. A ray tracing unit 1408is implemented on the GPU 1404. The components of the computer systemcan communicate with each other via a communications bus 1418. The raytracing unit 1408 may operate with part of the memory 1406 to implementthe ray tracing system 300 or the ray tracing system 900 describedabove. In some examples the ray tracing system may be implementedseparately from the GPU 1404.

The ray tracing systems 300 and 900 are shown as comprising a number offunctional blocks. This is schematic only and is not intended to definea strict division between different logic elements of such entities.Each functional block may be provided in any suitable manner. It is tobe understood that intermediate values described herein as being formedby a ray tracing system need not be physically generated by the raytracing system at any point and may merely represent logical valueswhich conveniently describe the processing performed by the ray tracingsystem between its input and output.

The ray tracing systems described herein may be embodied in hardware onan integrated circuit. The ray tracing systems described herein may beconfigured to perform any of the methods described herein. Generally,any of the functions, methods, techniques or components described abovecan be implemented in software, firmware, hardware (e.g., fixed logiccircuitry), or any combination thereof. The terms “module,”“functionality,” “component”, “element”, “unit”, “block” and “logic” maybe used herein to generally represent software, firmware, hardware, orany combination thereof. In the case of a software implementation, themodule, functionality, component, element, unit, block or logicrepresents program code that performs the specified tasks when executedon a processor. The algorithms and methods described herein could beperformed by one or more processors executing code that causes theprocessor(s) to perform the algorithms/methods. Examples of acomputer-readable storage medium include a random-access memory (RAM),read-only memory (ROM), an optical disc, flash memory, hard disk memory,and other memory devices that may use magnetic, optical, and othertechniques to store instructions or other data and that can be accessedby a machine.

The terms computer program code and computer readable instructions asused herein refer to any kind of executable code for processors,including code expressed in a machine language, an interpreted languageor a scripting language. Executable code includes binary code, machinecode, bytecode, code defining an integrated circuit (such as a hardwaredescription language or netlist), and code expressed in a programminglanguage code such as C, Java or OpenCL. Executable code may be, forexample, any kind of software, firmware, script, module or librarywhich, when suitably executed, processed, interpreted, compiled,executed at a virtual machine or other software environment, cause aprocessor of the computer system at which the executable code issupported to perform the tasks specified by the code.

A processor, computer, or computer system may be any kind of device,machine or dedicated circuit, or collection or portion thereof, withprocessing capability such that it can execute instructions. A processormay be any kind of general purpose or dedicated processor, such as aCPU, GPU, System-on-chip, state machine, media processor, anapplication-specific integrated circuit (ASIC), a programmable logicarray, a field-programmable gate array (FPGA), or the like. A computeror computer system may comprise one or more processors.

It is also intended to encompass software which defines a configurationof hardware as described herein, such as HDL (hardware descriptionlanguage) software, as is used for designing integrated circuits, or forconfiguring programmable chips, to carry out desired functions. That is,there may be provided a computer readable storage medium having encodedthereon computer readable program code in the form of an integratedcircuit definition dataset that when processed (i.e. run) in anintegrated circuit manufacturing system configures the system tomanufacture a ray tracing system configured to perform any of themethods described herein, or to manufacture a ray tracing systemcomprising any apparatus described herein. An integrated circuitdefinition dataset may be, for example, an integrated circuitdescription.

Therefore, there may be provided a method of manufacturing, at anintegrated circuit manufacturing system, a ray tracing system asdescribed herein. Furthermore, there may be provided an integratedcircuit definition dataset that, when processed in an integrated circuitmanufacturing system, causes the method of manufacturing a ray tracingsystem to be performed.

An integrated circuit definition dataset may be in the form of computercode, for example as a netlist, code for configuring a programmablechip, as a hardware description language defining hardware suitable formanufacture in an integrated circuit at any level, including as registertransfer level (RTL) code, as high-level circuit representations such asVerilog or VHDL, and as low-level circuit representations such as OASIS®and GDSII. Higher level representations which logically define hardwaresuitable for manufacture in an integrated circuit (such as RTL) may beprocessed at a computer system configured for generating a manufacturingdefinition of an integrated circuit in the context of a softwareenvironment comprising definitions of circuit elements and rules forcombining those elements in order to generate the manufacturingdefinition of an integrated circuit so defined by the representation. Asis typically the case with software executing at a computer system so asto define a machine, one or more intermediate user steps (e.g. providingcommands, variables etc.) may be required in order for a computer systemconfigured for generating a manufacturing definition of an integratedcircuit to execute code defining an integrated circuit so as to generatethe manufacturing definition of that integrated circuit.

An example of processing an integrated circuit definition dataset at anintegrated circuit manufacturing system so as to configure the system tomanufacture a ray tracing system will now be described with respect toFIG. 15 .

FIG. 15 shows an example of an integrated circuit (IC) manufacturingsystem 1502 which is configured to manufacture a ray tracing system asdescribed in any of the examples herein. In particular, the ICmanufacturing system 1502 comprises a layout processing system 1504 andan integrated circuit generation system 1506. The IC manufacturingsystem 1502 is configured to receive an IC definition dataset (e.g.defining a ray tracing system as described in any of the examplesherein), process the IC definition dataset, and generate an IC accordingto the IC definition dataset (e.g. which embodies a ray tracing systemas described in any of the examples herein). The processing of the ICdefinition dataset configures the IC manufacturing system 1502 tomanufacture an integrated circuit embodying a ray tracing system asdescribed in any of the examples herein.

The layout processing system 1504 is configured to receive and processthe IC definition dataset to determine a circuit layout. Methods ofdetermining a circuit layout from an IC definition dataset are known inthe art, and for example may involve synthesising RTL code to determinea gate level representation of a circuit to be generated, e.g. in termsof logical components (e.g. NAND, NOR, AND, OR, MUX and FLIP-FLOPcomponents). A circuit layout can be determined from the gate levelrepresentation of the circuit by determining positional information forthe logical components. This may be done automatically or with userinvolvement in order to optimise the circuit layout. When the layoutprocessing system 1504 has determined the circuit layout it may output acircuit layout definition to the IC generation system 1506. A circuitlayout definition may be, for example, a circuit layout description.

The IC generation system 1506 generates an IC according to the circuitlayout definition, as is known in the art. For example, the ICgeneration system 1506 may implement a semiconductor device fabricationprocess to generate the IC, which may involve a multiple-step sequenceof photo lithographic and chemical processing steps during whichelectronic circuits are gradually created on a wafer made ofsemiconducting material. The circuit layout definition may be in theform of a mask which can be used in a lithographic process forgenerating an IC according to the circuit definition. Alternatively, thecircuit layout definition provided to the IC generation system 1506 maybe in the form of computer-readable code which the IC generation system1506 can use to form a suitable mask for use in generating an IC.

The different processes performed by the IC manufacturing system 1502may be implemented all in one location, e.g. by one party.Alternatively, the IC manufacturing system 1502 may be a distributedsystem such that some of the processes may be performed at differentlocations, and may be performed by different parties. For example, someof the stages of: (i) synthesising RTL code representing the ICdefinition dataset to form a gate level representation of a circuit tobe generated, (ii) generating a circuit layout based on the gate levelrepresentation, (iii) forming a mask in accordance with the circuitlayout, and (iv) fabricating an integrated circuit using the mask, maybe performed in different locations and/or by different parties.

In other examples, processing of the integrated circuit definitiondataset at an integrated circuit manufacturing system may configure thesystem to manufacture a ray tracing system without the IC definitiondataset being processed so as to determine a circuit layout. Forinstance, an integrated circuit definition dataset may define theconfiguration of a reconfigurable processor, such as an FPGA, and theprocessing of that dataset may configure an IC manufacturing system togenerate a reconfigurable processor having that defined configuration(e.g. by loading configuration data to the FPGA).

In some embodiments, an integrated circuit manufacturing definitiondataset, when processed in an integrated circuit manufacturing system,may cause an integrated circuit manufacturing system to generate adevice as described herein. For example, the configuration of anintegrated circuit manufacturing system in the manner described abovewith respect to FIG. 15 by an integrated circuit manufacturingdefinition dataset may cause a device as described herein to bemanufactured.

In some examples, an integrated circuit definition dataset could includesoftware which runs on hardware defined at the dataset or in combinationwith hardware defined at the dataset. In the example shown in FIG. 15 ,the IC generation system may further be configured by an integratedcircuit definition dataset to, on manufacturing an integrated circuit,load firmware onto that integrated circuit in accordance with programcode defined at the integrated circuit definition dataset or otherwiseprovide program code with the integrated circuit for use with theintegrated circuit.

The implementation of concepts set forth in this application in devices,apparatus, modules, and/or systems (as well as in methods implementedherein) may give rise to performance improvements when compared withknown implementations. The performance improvements may include one ormore of increased computational performance, reduced latency, increasedthroughput, and/or reduced power consumption. During manufacture of suchdevices, apparatus, modules, and systems (e.g. in integrated circuits)performance improvements can be traded-off against the physicalimplementation, thereby improving the method of manufacture. Forexample, a performance improvement may be traded against layout area,thereby matching the performance of a known implementation but usingless silicon. This may be done, for example, by reusing functionalblocks in a serialised fashion or sharing functional blocks betweenelements of the devices, apparatus, modules and/or systems. Conversely,concepts set forth in this application that give rise to improvements inthe physical implementation of the devices, apparatus, modules, andsystems (such as reduced silicon area) may be traded for improvedperformance. This may be done, for example, by manufacturing multipleinstances of a module within a predefined area budget.

The applicant hereby discloses in isolation each individual featuredescribed herein and any combination of two or more such features, tothe extent that such features or combinations are capable of beingcarried out based on the present specification as a whole in the lightof the common general knowledge of a person skilled in the art,irrespective of whether such features or combinations of features solveany problems disclosed herein. In view of the foregoing description itwill be evident to a person skilled in the art that variousmodifications may be made within the scope of the invention.

What is claimed is:
 1. A computer-implemented method of performing intersection testing in a ray tracing system to test a bundle of rays for intersection with a box, the method comprising: for each of a plurality of silhouette edges of the box, determining whether a vector providing a bound to the bundle of rays passes inside or outside of the silhouette edge; and using results of determining, for each of the silhouette edges, whether the vector passes inside or outside of the silhouette edge, to determine an intersection testing result for the bundle of rays with respect to the box.
 2. The method of claim 1, further comprising identifying the silhouette edges of the box from the perspective of the bundle of rays.
 3. The method of claim 1, further comprising, for each of the silhouette edges, obtaining components of the vector providing a bound to the bundle of rays.
 4. The method of claim 3, wherein the obtained components of the vector providing a bound to the bundle of rays are the same as components of a direction vector of one of the rays of the bundle.
 5. The method of claim 1, wherein the method comprises, for each of the silhouette edges, determining whether a single vector providing a single bound to the bundle of rays passes inside or outside of the silhouette edge.
 6. The method of claim 3, wherein said obtained components of the vector providing a bound to the bundle of rays are chosen from a set of component values comprising a minimum component value and a maximum component value in each dimension of direction vectors of the rays in the bundle of rays.
 7. The method of claim 1, wherein for each of the silhouette edges, the vector for which it is determined whether the vector passes inside or outside of the silhouette edge is the only vector for which a determination is made for the bundle of rays as to whether the vector passes inside or outside of the silhouette edge.
 8. The method of claim 1, wherein the intersection testing result for the bundle of rays with respect to the box is determined using said results of determining, for each of the silhouette edges, whether the vector passes inside or outside of the silhouette edge, and without using any other results of determining whether any other vectors pass inside or outside of the silhouette edges.
 9. The method of claim 1, wherein the box is an axis-aligned bounding box.
 10. The method of claim 1, wherein all of the rays of the bundle of rays have the same origin and wherein, for each of the silhouette edges, said determining whether the vector passes inside or outside of the silhouette edge comprises performing a comparison in accordance with (p_(o,i)−o_(i))d_(j)<(p_(o,j)−o_(j))d_(i), wherein p_(o,i) is the i^(th) component of a point on a first plane representing a first of the sides of the box which forms the silhouette edge, p_(o,j) is the j^(th) component of a point on a second plane representing a second of the sides of the box which forms the silhouette edge, o_(i) and o_(j) are the i^(th) and j^(th) components of the origin of the rays of the bundle of rays, and d_(i) and d_(j) are the obtained i^(th) and j^(th) components of the vector providing a bound to the bundle of rays.
 11. The method of claim 1, wherein it is not the case that all of the rays of the bundle of rays have the same origin and wherein, for each of the silhouette edges, said determining whether the vector passes inside or outside of the silhouette edge comprises performing a comparison in accordance with (p_(o,i)−o_(i,[min,max]))d_(j)<(p_(o,j)−o_(j,[min,max]))d_(i), wherein p_(o,i) is the i^(th) component of a point on a first plane representing a first of the sides of the box which forms the silhouette edge, p_(o,j) is the j^(th) component of a point on a second plane representing a second of the sides of the box which forms the silhouette edge, o_(i[min,max]) is either the minimum or the maximum of the i^(th) components of the origins of the rays of the bundle of rays, o_(j[min,max]) is either the minimum or the maximum of the j^(th) components of the origins of the rays of the bundle of rays, and d_(i) and d_(j) are the obtained i^(th) and j^(th) components of the vector providing a bound to the bundle of rays.
 12. The method of claim 1, further comprising: receiving rays; and constructing bundles of rays from the received rays to be tested for intersection with the box, wherein said constructing bundles of rays comprises grouping together received rays based on their similarity; wherein said constructing bundles of rays comprises: maintaining a set of open bundles to which new rays can be added, and for each of the received rays: determining a level of similarity of the received ray with each of the open bundles, identifying a best match open bundle of said set of open bundles for the received ray based on the determined levels of similarity, and in response to the determined level of similarity of the received ray with the best match open bundle being above a threshold, adding the received ray to the best match open bundle.
 13. The method of claim 12, further comprising, for each of the received rays: in response to the determined level of similarity for the best match open bundle being below the threshold, creating a new bundle and adding the received ray to the new bundle.
 14. A ray tracing system comprising: a tester circuit configured to perform intersection testing on a bundle of rays with respect to a box by: for each of a plurality of silhouette edges of the box, determining whether a vector providing a bound to the bundle of rays passes inside or outside of the silhouette edge, and using results of determining, for each of the silhouette edges, whether the vector passes inside or outside of the silhouette edge, to determine an intersection testing result for the bundle of rays with respect to the box.
 15. The ray tracing system of claim 14, wherein for each of the silhouette edges said vector provides an external bound to the bundle of rays with respect to said silhouette edge, such that if it does not pass outside the silhouette edge then it is known that none of the rays of the bundle pass outside said silhouette edge.
 16. The ray tracing system of claim 15, wherein the tester circuit is configured such that if it is determined that, for each of the silhouette edges, the vector passes inside the respective silhouette edge, then the intersection testing result for the bundle of rays with respect to the box is that all of the rays in the bundle of rays intersect the box; wherein the tester circuit is configured such that if it is determined that, for one or more of the silhouette edges, the vector passes outside the respective silhouette edge, then the intersection testing result for the bundle of rays with respect to the box is not that all of the rays in the bundle of rays intersect the box; and wherein the tester circuit is configured to, if the intersection testing result for the bundle of rays with respect to the box is not that all of the rays in the bundle of rays intersect the box, determine whether any of the rays in the bundle of rays intersect the box.
 17. The ray tracing system of claim 14, wherein for each of the silhouette edges said vector provides an internal bound to the bundle of rays with respect to said silhouette edge, such that if it does not pass inside the silhouette edge then it is known that none of the rays of the bundle pass inside said silhouette edge.
 18. The ray tracing system of claim 17, wherein the tester circuit is configured such that if it is determined that, for each of the silhouette edges, the vector passes inside the respective silhouette edge, then the intersection testing result for the bundle of rays with respect to the box is not that all of the rays in the bundle of rays miss the box; wherein the tester circuit is configured such that if it is determined that, for one or more of the silhouette edges, the vector passes outside the respective silhouette edge, then the intersection testing result for the bundle of rays with respect to the box is that all of the rays in the bundle of rays miss the box; and wherein the tester circuit is configured to, if the intersection testing result for the bundle of rays with respect to the box is not that all of the rays in the bundle of rays miss the box, determine which of the rays in the bundle of rays intersect the box.
 19. The ray tracing system of claim 14, wherein the tester circuit is further configured to: perform a direction check to determine whether the box is behind an origin of the bundle of rays, wherein if the direction check determines that the box is behind the origin of the bundle of rays then the intersection testing result is that the bundle of rays misses the box; and/or perform a distance check to determine whether the bundle of rays terminates at a point in front of the box, wherein if the distance check determines that the bundle of rays terminates at a point in front of the box then the intersection testing result is that the bundle of rays misses the box.
 20. A non-transitory computer readable storage medium having stored thereon computer program code for performing a method of performing intersection testing in a ray tracing system to test a bundle of rays for intersection with a box, the method comprising: for each of a plurality of silhouette edges of the box, determining whether a vector providing a bound to the bundle of rays passes inside or outside of the silhouette edge; and using results of determining, for each of the silhouette edges, whether the vector passes inside or outside of the silhouette edge, to determine an intersection testing result for the bundle of rays with respect to the box. 